Threading code review please.

[Jeff Roberson]

I'm going to reply to the threads on 1:1 vs M:N tomorrow.  I'd like to
request that people actually read the patch and give me feedback on the
code and not the approach.

I have no outstanding behavior problems with mozilla.  It actually runs
much faster now with libthr in place of libc_r.  On pages with LOTS of
images it scrolls much smoother.  I suspect its the amount of io waits.

Anyway, since this is coming together so well I'd like to get it commited
soon so people can start giving me bug reports.  I have another full days
worth of work to clear up the issues that I know of.  I'll probably post
the library source tomorrow.

Cheers,
Jeff