[Swan] SIGINT and xauth.c

[D. Hugh Redelmeier]

| From: D. Hugh Redelmeier <hugh at mimosa.com>

| If a SIGINT were delivered to another thread, but there was an xauth
| thread running, the xauth signal handler would catch the signal.  As
| it is currently written, that signal handler calls lsw_abort if it
| doesn't find the thread in xauth.c's thread table.

I would bet that lsw_abort uses parts of the library that are not
re-entrant or perhaps even thread-safe.  So the signal handler should
not call lsw_abort.

According to "Async-signal-safe functions" in signal(7), abort() itself is 
safe to call in a signal handler.  So too is write(2).  This is a POSIX 
feature.