Only allow one <namespace/> element per <repository/> (#560419)

Only allow one <namespace/> element per <repository/> (#560419)

The logic in girparser.c didn't work very well if there were multiple
<namespace/> nodes within a single <repository/> (context->namespace
was always the overall filename and not the the name specified in the
<namespace/> element for one thing; this would cause aliases to
be mis-prefixed in include modules.) Also check that the "name" in
the <namespace/> node matches the filename.

svn path=/trunk/; revision=902