compositor-xrender: add new atom - METACITY_WINDOW_HAVE_SHADOW

Based on metacity commit: c52cd2e1d6ae50627bc9056ea6eae773e2aedfe5
From: Alberts Muktupāvels <alberts.muktupavels@gmail.com>
theme-viewer: stop using gtk_misc_set_alignment for Gtk+3

Based on metacity commit: 99bfe2d27c6babeeea3539b990505895750d3541
From: Alberts Muktupāvels <alberts.muktupavels@gmail.com>
Clean up code to find themes

Simplify code to find the right theme to load and loading it by
moving all the loading code into a load_theme() helper function,
and making meta_load_theme() use that as it searches through the
directories.

Look for old-version themes even when loading relative to the
working in debug mode. Don't unnecessarily duplicate and then free
info->theme_file and info->theme_dir.

http://bugzilla.gnome.org/show_bug.cgi?id=592503

NOTE: Patch copied from mutter and adapted for metacity.

Based on metacity commit: bc45c9b68849687d456ec339588d15a63c391046
From: Alberts Muktupāvels <alberts.muktupavels@gmail.com>
Add in XDG_USER_DATA_DIR when looking for themes

Based off metacity commit: 52a524ee4a7e14d99451ea3f596b353ddf7957d4
From: Jasper St. Pierre <jstpierre@mecheye.net>
Make sure to always call va_end

Based on metacity commit: b235d3e78670e30a55f3f746f13003577988bed6
From: Jasper St. Pierre <jstpierre@mecheye.net>