Make the current code compile again under GTK1.

Apparently I haven't tested this compile mode in a while: I had a
couple of compile errors due to new code not properly #ifdeffed (the
true-colour mode has to be effectively disabled in the palette-based
GTK1 graphics model) and one for an unused static function
(get_monitor_geometry is only used in GTK2 and above, and with -Werror
that means I mustn't even _define_ it in GTK1).

With these changes, I still didn't get a clean compile unless I also
configured CFLAGS=-std=gnu89, due to the GTK1 headers having an
outdated set of ifdefs to figure out the compiler's semantics of
'inline'. (They seem to expect old-style gcc, which inconveniently
treats 'inline' and 'extern inline' more or less the opposite way
round from the version standardised by C99.)

unix/gtkwin.c

@@ -3039,11 +3039,16 @@ static void draw_set_colour(struct draw_ctx *dctx, int col, int dim)
 #ifdef DRAW_TEXT_GDK
     if (dctx->uctx.type == DRAWTYPE_GDK) {
         if (dim) {
+#if GTK_CHECK_VERSION(2,0,0)
             GdkColor color;
             color.red =   dctx->inst->cols[col].red   * 2 / 3;
             color.green = dctx->inst->cols[col].green * 2 / 3;
             color.blue =  dctx->inst->cols[col].blue  * 2 / 3;
             gdk_gc_set_rgb_fg_color(dctx->uctx.u.gdk.gc, &color);
+#else
+            /* Poor GTK1 fallback */
+            gdk_gc_set_foreground(dctx->uctx.u.gdk.gc, &dctx->inst->cols[col]);
+#endif
         } else {
             gdk_gc_set_foreground(dctx->uctx.u.gdk.gc, &dctx->inst->cols[col]);
         }
@@ -3064,6 +3069,7 @@ static void draw_set_colour_rgb(struct draw_ctx *dctx, optionalrgb orgb,
 {
 #ifdef DRAW_TEXT_GDK
     if (dctx->uctx.type == DRAWTYPE_GDK) {
+#if GTK_CHECK_VERSION(2,0,0)
 	GdkColor color;
 	color.red =   orgb.r * 256;
 	color.green = orgb.g * 256;
@@ -3074,6 +3080,10 @@ static void draw_set_colour_rgb(struct draw_ctx *dctx, optionalrgb orgb,
             color.blue  = color.blue  * 2 / 3;
         }
 	gdk_gc_set_rgb_fg_color(dctx->uctx.u.gdk.gc, &color);
+#else
+        /* Poor GTK1 fallback */
+        gdk_gc_set_foreground(dctx->uctx.u.gdk.gc, &dctx->inst->cols[256]);
+#endif
     }
 #endif
 #ifdef DRAW_TEXT_CAIRO
@@ -4374,6 +4384,7 @@ static void start_backend(struct gui_data *inst)
     gtk_widget_set_sensitive(inst->restartitem, FALSE);
 }
 
+#if GTK_CHECK_VERSION(2,0,0)
 static void get_monitor_geometry(GtkWidget *widget, GdkRectangle *geometry)
 {
 #if GTK_CHECK_VERSION(3,4,0)
@@ -4397,6 +4408,7 @@ static void get_monitor_geometry(GtkWidget *widget, GdkRectangle *geometry)
     geometry->height = gdk_screen_height();
 #endif
 }
+#endif
 
 struct gui_data *new_session_window(Conf *conf, const char *geometry_string)
 {