[gnome-tweak-tool] Print more useful error for missing schemas

[John Stowers <jstowers src gnome org>]

commit 96ca58e9034c0a4ae6d84ca53e37bc1d50ec0923
Author: John Stowers <john stowers gmail com>
Date:   Thu Nov 24 09:55:38 2011 +1300

    Print more useful error for missing schemas

 gtweak/gsettings.py |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)
---
diff --git a/gtweak/gsettings.py b/gtweak/gsettings.py
index ca7020f..9ab8749 100644
--- a/gtweak/gsettings.py
+++ b/gtweak/gsettings.py
@@ -31,7 +31,9 @@ class _GSettingsSchema:
             schema_filename = schema_name + ".gschema.xml"
 
         schema_path = os.path.join(schema_dir, schema_filename)
-        assert(os.path.exists(schema_path))
+        if not os.path.exists(schema_path):
+            logging.critical("Could not find schema %s" % schema_path)
+            assert(False)
 
         self._schema_name = schema_name
         self._schema = {}