[DotGNU]Threading

[Thong \(Tum\) Nguyen]

Yah, finally submitted the patch :-).

I've spent the last couple of sleepless days trying to debug some
problems with the threading support that popped up when I installed the
GC.  It seems pretty stable now.

I've implemented two different types of monitors:  object header based
and hashtable based with object-header-based the default.  You can
enable hashtable based monitors by compiling with USE_HASHING_MONITORS.
Hashtable based monitors appear to be around 3 times slower which isn't
really that bad considering it'll save 4 bytes per object :-).

The Thread, WaitHandle and Monitor objects now all work :D.

^Tum