MFC r198507:

MFC r198507:
Use kern_sigprocmask() instead of direct manipulation of td_sigmask to
reschedule newly blocked signals.

MFC r198590:
Trapsignal() calls kern_sigprocmask() when delivering catched signal
with proc lock held.

MFC r198670:
For trapsignal() and postsig(), kern_sigprocmask() is called with
both process lock and curproc->p_sigacts->ps_mtx locked. Prevent lock
recursion on ps_mtx in reschedule_signals().

git-svn-id: svn://svn.freebsd.org/base/stable/8@200722 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f