Initial support for gdb python macros

This includes support for gobject pointer pretty printing and
signal frame compression in backtraces.

https://bugzilla.gnome.org/show_bug.cgi?id=595619

gobject/libgobject-gdb.py.in

@@ -0,0 +1,10 @@
+import sys
+import gdb
+
+# Update module path.
+dir = '@datadir@/glib-2.0/gdb'
+if not dir in sys.path:
+    sys.path.insert(0, dir)
+
+from gobject import register
+register (gdb.current_objfile ())