the signal mask and pending signals of the calling thread. These
are stored in userland in libpthread.
There is a small race condition in this patch which could cause
problems if a signal arrives after setting the (kernel) signal
mask and before exec'ing. The thread's set of pending signals
also are not yet installed in the exec'd process. Both of these
will be corrected with the addition of a special syscall.
Reported & Tested by: Joost Bekkers <joost at jodocus dot org>
Reviewed by: julian, davidxu
