Inside glibtransformer, we now look at structures ending in "Class" and
see if they have an associated GlibObject (i.e. a structure of the same
name without the "Class" suffix).  If found, pair them up.

The .gir file for <class> gains an attribute denoting its associated
class struct.  Any <record> many now have a glib:is-class-struct-for
annotation which tells which (if any) <class> for which it defines the
layout.

In the .typelib, we record the association between the class and
its structure.  Generic structures however just have a boolean
saying whether they're a class struct.  (Going from a generic class
struct to its class should not be necessary).

Finally, we expose GIRepository APIs to access both bits of information
from the .typelib.

svn path=/trunk/; revision=1088