Use C99 bool within source modules.

This is the main bulk of this boolification work, but although it's
making the largest actual change, it should also be the least
disruptive to anyone interacting with this code base downstream of me,
because it doesn't modify any interface between modules: all the
inter-module APIs were updated one by one in the previous commits.
This just cleans up the code within each individual source file to use
bool in place of int where I think that makes things clearer.

gtk.c

@@ -167,12 +167,14 @@ struct frontend {
 #endif
     int ncolours;
     int bbox_l, bbox_r, bbox_u, bbox_d;
-    int timer_active, timer_id;
+    bool timer_active;
+    int timer_id;
     struct timeval last_time;
     struct font *fonts;
     int nfonts, fontsize;
     config_item *cfg;
-    int cfg_which, cfgret;
+    int cfg_which;
+    bool cfgret;
     GtkWidget *cfgbox;
     void *paste_data;
     int paste_data_len;
@@ -182,12 +184,12 @@ struct frontend {
     char *filesel_name;
 #endif
     GSList *preset_radio;
-    int preset_threaded;
+    bool preset_threaded;
     GtkWidget *preset_custom;
     GtkWidget *copy_menu_item;
 #if !GTK_CHECK_VERSION(3,0,0)
-    int drawing_area_shrink_pending;
-    int menubar_is_local;
+    bool drawing_area_shrink_pending;
+    bool menubar_is_local;
 #endif
 #if GTK_CHECK_VERSION(3,0,0)
     /*
@@ -219,7 +221,7 @@ struct frontend {
      * happen, the window's size_allocate handler does a fallback
      * puzzle resize when it sees this flag still set to true.
      */
-    int awaiting_resize_ack;
+    bool awaiting_resize_ack;
 #endif
 };
 
@@ -494,7 +496,7 @@ static void clear_backing_store(frontend *fe)
 }
 
 static void wipe_and_maybe_destroy_cairo(frontend *fe, cairo_t *cr,
-                                         int destroy)
+                                         bool destroy)
 {
     cairo_set_source_rgb(cr, fe->colours[0], fe->colours[1], fe->colours[2]);
     cairo_paint(cr);
@@ -536,9 +538,9 @@ static void setup_backing_store(frontend *fe)
 #endif
 }
 
-static int backing_store_ok(frontend *fe)
+static bool backing_store_ok(frontend *fe)
 {
-    return (!!fe->image);
+    return fe->image != NULL;
 }
 
 static void teardown_backing_store(frontend *fe)
@@ -1459,7 +1461,7 @@ static void window_destroy(GtkWidget *widget, gpointer data)
     gtk_main_quit();
 }
 
-static int win_key_press(GtkWidget *widget, GdkEventKey *event, gpointer data)
+static gint win_key_press(GtkWidget *widget, GdkEventKey *event, gpointer data)
 {
     GObject *cancelbutton = G_OBJECT(data);
 
@@ -1494,8 +1496,8 @@ static void align_label(GtkLabel *label, double x, double y)
 }
 
 #if GTK_CHECK_VERSION(3,0,0)
-int message_box(GtkWidget *parent, const char *title, const char *msg,
-                int centre, int type)
+bool message_box(GtkWidget *parent, const char *title, const char *msg,
+                 bool centre, int type)
 {
     GtkWidget *window;
     gint ret;
@@ -1524,8 +1526,8 @@ static void msgbox_button_clicked(GtkButton *button, gpointer data)
     gtk_widget_destroy(GTK_WIDGET(data));
 }
 
-int message_box(GtkWidget *parent, const char *title, const char *msg,
-                int centre, int type)
+bool message_box(GtkWidget *parent, const char *title, const char *msg,
+                 bool centre, int type)
 {
     GtkWidget *window, *hbox, *text, *button;
     char *titles;
@@ -1617,7 +1619,7 @@ static void config_cancel_button_clicked(GtkButton *button, gpointer data)
     gtk_widget_destroy(fe->cfgbox);
 }
 
-static int editbox_key(GtkWidget *widget, GdkEventKey *event, gpointer data)
+static gint editbox_key(GtkWidget *widget, GdkEventKey *event, gpointer data)
 {
     /*
      * GtkEntry has a nasty habit of eating the Return key, which
@@ -1664,7 +1666,7 @@ static void droplist_sel(GtkComboBox *combo, gpointer data)
     i->u.choices.selected = gtk_combo_box_get_active(combo);
 }
 
-static int get_config(frontend *fe, int which)
+static bool get_config(frontend *fe, int which)
 {
     GtkWidget *w, *table, *cancel;
     GtkBox *content_box, *button_box;
@@ -1953,13 +1955,13 @@ static void changed_preset(frontend *fe)
      * Update the greying on the Copy menu option.
      */
     if (fe->copy_menu_item) {
-	int enabled = midend_can_format_as_text_now(fe->me);
+        bool enabled = midend_can_format_as_text_now(fe->me);
 	gtk_widget_set_sensitive(fe->copy_menu_item, enabled);
     }
 }
 
 #if !GTK_CHECK_VERSION(3,0,0)
-static gboolean not_size_allocated_yet(GtkWidget *w)
+static bool not_size_allocated_yet(GtkWidget *w)
 {
     /*
      * This function tests whether a widget has not yet taken up space
@@ -2084,7 +2086,7 @@ static void menu_preset_event(GtkMenuItem *menuitem, gpointer data)
 }
 
 GdkAtom compound_text_atom, utf8_string_atom;
-int paste_initialised = false;
+bool paste_initialised = false;
 
 static void set_selection(frontend *fe, GdkAtom selection)
 {
@@ -2201,7 +2203,7 @@ static char *file_selector(frontend *fe, const char *title, int save)
 
 #else
 
-static char *file_selector(frontend *fe, const char *title, int save)
+static char *file_selector(frontend *fe, const char *title, bool save)
 {
     char *filesel_name = NULL;
 
@@ -2906,16 +2908,17 @@ int main(int argc, char **argv)
 {
     char *pname = argv[0];
     char *error;
-    int ngenerate = 0, print = false, px = 1, py = 1;
-    int time_generation = false, test_solve = false, list_presets = false;
-    int soln = false, colour = false;
+    int ngenerate = 0, px = 1, py = 1;
+    bool print = false;
+    bool time_generation = false, test_solve = false, list_presets = false;
+    bool soln = false, colour = false;
     float scale = 1.0F;
     float redo_proportion = 0.0F;
     const char *savefile = NULL, *savesuffix = NULL;
     char *arg = NULL;
     int argtype = ARG_EITHER;
     char *screenshot_file = NULL;
-    int doing_opts = true;
+    bool doing_opts = true;
     int ac = argc;
     char **av = argv;
     char errbuf[500];