Introduce a versioning mechanism, and an `About' box in all front

ends. Versioning will be done solely by Subversion revision number,
since development on these puzzles is very incremental and gradual
and there don't tend to be obvious points to place numbered
releases.

[originally from svn r5781]

Recipe

@@ -14,7 +14,7 @@
 !makefile osx Makefile.osx
 
 WINDOWS  = windows user32.lib gdi32.lib comctl32.lib
-COMMON   = midend misc malloc random
+COMMON   = midend misc malloc random version
 NET      = net tree234
 NETSLIDE = netslide tree234
 
@@ -84,3 +84,41 @@ Puzzles.dmg: Puzzles
 # be built on a regular basis.
 nullgame : [X] gtk COMMON nullgame
 nullgame : [G] WINDOWS COMMON nullgame
+
+# Version management.
+!begin vc
+version.obj: *.c *.h
+	cl $(VER) $(CFLAGS) /c version.c
+!end
+!specialobj vc version
+!begin cygwin
+version.o: FORCE
+FORCE:
+	$(CC) $(COMPAT) $(XFLAGS) $(CFLAGS) $(VER) -c version.c
+!end
+!specialobj cygwin version
+# For Unix, we also need the gross MD5 hack that causes automatic
+# version number selection in release source archives.
+!begin gtk
+version.o: FORCE;
+FORCE:
+	if test -z "$(VER)" && md5sum -c manifest; then \
+		$(CC) $(COMPAT) $(XFLAGS) $(CFLAGS) `cat version.def` -c version.c; \
+	else \
+		$(CC) $(COMPAT) $(XFLAGS) $(CFLAGS) $(VER) -c version.c; \
+	fi
+!end
+!specialobj gtk version
+# For OS X, this is made more fiddly by the fact that we don't have
+# md5sum readily available. We do, however, have `md5 -r' which
+# generates _nearly_ the same output, but it has no check function.
+!begin osx
+version.o: FORCE;
+FORCE:
+	if test -z "$(VER)" && test -f manifest && (md5 -r `awk '{print $$2}' manifest` | diff -w manifest -); then \
+		$(CC) $(COMPAT) $(XFLAGS) $(CFLAGS) `cat version.def` -c version.c; \
+	else \
+		$(CC) $(COMPAT) $(XFLAGS) $(CFLAGS) $(VER) -c version.c; \
+	fi
+!end
+!specialobj osx version