Rename gdb macros with _gdb suffix to avoid ns clashes

glib installs a gdb helper file named `glib.py`.
Then the "hook" file updates `sys.path` and does `import glib`.

This will fail if glib has already been imported into gdb, say
using `from gi.repository import GLib`.  This is due to a namespace clash.

One fix would be to rename the gdb helper files to not clash with
other Python modules.  This should be done for all such helper files.

https://bugzilla.gnome.org/show_bug.cgi?id=760186

gobject/libgobject-gdb.py.in

@@ -6,5 +6,5 @@ dir_ = '@datadir@/glib-2.0/gdb'
 if not dir_ in sys.path:
     sys.path.insert(0, dir_)
 
-from gobject import register
+from gobject_gdb import register
 register (gdb.current_objfile ())