This patch updates Python/thread_pthread.h to mask all
signals for any thread created.  This will keep all
signals masked for any thread that isn't the initial
thread.  For Solaris and Linux, the two platforms I was
able to test it on, it solves bug #465673 (pthreads
need signal protection) and probably will solve bug
#219772 (Interactive InterPreter+ Thread -> core dump
at exit).

I'd be great if this could get some testing on other
platforms, especially HP-UX pre 11.00 and post 11.00,
as I had to make some guesses for the DCE thread case.
AIX is also a concern as I saw some mention of using
sigthreadmask() as a pthread_sigmask() equivalent, but
this patch doesn't use sigthreadmask().  I don't have
access to AIX.

Note that thread_pthread.h.orig in this patch is the
unmodified version from the Python2.1 release.