queried for a missing extension (such as the XiG vidmode one that most
 people don't have), and default Xlib behaviour is to write notification to
 stderr, this tends to generate incorrect bug reports.

Since we'll actually deal with the missing extension when querying for it,
 we ignore these errors in our hook. The rest continue to pass through to
 the default handler.

Fixes Bugzilla #42.

--ryan.

--HG--
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/trunk%401251