* exceptions.cc (stackdump): Make global.

* exceptions.cc (stackdump): Make global.
(signal_exit): Move to sigproc.cc.
* sigproc.cc (signal_exit): Move here.  Declare stackdump extern.  Set
my_sendsig to indicate that signals are no longer available.
(my_readsig): Make Static again.
(sig_send): Interpret ERROR_BROKEN_PIPE as ESRCH.  Remove special-case EACCESS
errno setting, just setting errno generally, even for "its_me" case.