Include the size and alignment of structures and unions in the typelib,
and add getter methods to retrieve them from GIStructInfo/GIUnionInfo.

* docs/typelib-format.txt girepository/gtypelib.h girepository/girnode.c
girepository/girmodule.c girepository/gtypelib.c: Add size and alignment
to StructBlob and UnionBlob.

* girepository/ginfo.c girepository/girepository.h:
Add g_[struct|union]_get[size|alignment]().

* test/offsets/gen-gitestoffsets: Test overall structure size and alignment.

svn path=/trunk/; revision=930