* sigproc.cc (pending_signals::retry): Declare new element.
(pending_signals::pending): Force an additional loop through wait_sig by
setting retry whenever this function is called.
(sig_send): Reorganize to wait for SIGHOLD at bottom.  Always add signal to
pending queue and work on whole queue rather than just the one signal.  Loop
when sigq.retry is set.  Fix long-broken check for SIGCHLD after queued
signals.
* sigproc.cc (wait_sig): Avoid uninitialized use of nb when retrying.
Consolidate two error messages into one.