Make it possible to have implementations in different toolkits.

Also, make it possible to share the headers.

gtk/OGHBox.m

@@ -0,0 +1,16 @@
+#import "OGHBox.h"
+
+@implementation OGHBox
+- init
+{
+	self = [super init];
+
+	widget = gtk_hbox_new(FALSE, 0);
+
+	g_signal_connect(G_OBJECT(widget), "destroy", G_CALLBACK(og_destroy),
+	    self);
+	[self retain];
+
+	return self;
+}
+@end