Bug 584423 – Add short/ushort support

Bug 584423 – Add short/ushort support

Add type tags for short and ushort, plus all of the requisite code needed
to utilize them in libgirepository.
Add support in the scanner's AST files.
Add test functions to the everything library and the expected gir file.

gtypelib.c constant validation fixed by Colin Walters <walters@verbum.org>