Add SF patch #468347 -- mask signals for non-main pthreads, by Jason Lowe:

Add SF patch #468347 -- mask signals for non-main pthreads, by Jason Lowe:

   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.