Added unit tests for Gtk+ testing utilities.

Added unit tests for Gtk+ testing utilities.

* gtk/tests/testing.c: added a sample test program that tests Gtk+ test
utility functions. some g_test_* related portions are disabled and need
to be enabled once Gtk+ depends on a new glib with the GLib testing
framework integrated.

* gtk/tests/Makefile.am: new subdirectory to include quick Gtk+ tests.
added exemplary test rules to run tests inside Xvfb. this needs to depend
on gtester for full fledged testing.

* gtk/Makefile.am: build gtk+/gtk/tests, define -DGTK_ENABLE_BROKEN when
collecting _get_type functions to catch e.g. gtk_text_get_type().

* configure.in: create gtk/tests/Makefile.in and gtk/tests/Makefile.

svn path=/trunk/; revision=19011