[DotGNU]New monitor implementation

[Thong \(Tum\) Nguyen]

Hiya folks,

I've just submitted an updated patch for threading.  The patch has the
following changes:

- Process now waits for user threads to exit before exiting itself.

- New monitor implementation :D.  The last one used GC memory to store
monitors which fails miserably if the object being locked is a primitive
array or string.  Took a while to figure out but the reason is because
arrays are allocated in memory the GC doesn't scan (for speed).  One
bonus is that the new implementation is faster and has good potential
for speed improvements.

Get it here :-).

https://savannah.gnu.org/patch/?func=detailpatch&patch_id=1657&group_id=
353

PS.  Still trying to get the relevant parts of pnet threadsafe so you
might get random core dumps (especially if you're using lots of threads
and thrashing them).

^Tum