Make it possible to have implementations in different toolkits.

Also, make it possible to share the headers.

gtk/OGWidget.m

@@ -0,0 +1,35 @@
+#include "OGWidget.h"
+
+void og_destroy(GtkWidget *widget, OGWidget *object)
+{
+	[object release];
+}
+
+@implementation OGWidget
+- init
+{
+	self = [super init];
+
+	@try {
+		if (isa == [OGWidget class])
+			@throw [OFNotImplementedException
+			    exceptionWithClass: isa
+				      selector: @selector(init)];
+	} @catch (id e) {
+		[self release];
+		@throw e;
+	}
+
+	return self;
+}
+
+- (void)show
+{
+	gtk_widget_show_all(widget);
+}
+
+- (void)hide
+{
+	gtk_widget_hide(widget);
+}
+@end