Move fgetline out into misc.c.

I'm about to want to use it outside the GTK front end.

misc.c

@@ -169,6 +169,25 @@ unsigned char *hex2bin(const char *in, int outlen)
     return ret;
 }
 
+char *fgetline(FILE *fp)
+{
+    char *ret = snewn(512, char);
+    int size = 512, len = 0;
+    while (fgets(ret + len, size - len, fp)) {
+	len += strlen(ret + len);
+	if (ret[len-1] == '\n')
+	    break;		       /* got a newline, we're done */
+	size = len + 512;
+	ret = sresize(ret, size, char);
+    }
+    if (len == 0) {		       /* first fgets returned NULL */
+	sfree(ret);
+	return NULL;
+    }
+    ret[len] = '\0';
+    return ret;
+}
+
 void game_mkhighlight_specific(frontend *fe, float *ret,
 			       int background, int highlight, int lowlight)
 {