The com_err library is now probably as thread-safe as it's going to get, on

The com_err library is now probably as thread-safe as it's going to get, on
UNIX; Windows still needs work....

* com_err.c: Include stdlib.h.
(com_err_hook_lock): New mutex.
(com_err_lock_hook_handle): New function.
(com_err_va, set_com_err_hook, reset_com_err_hook): Call com_err_finish_init,
and grab the lock.
* error_message.c: Don't include k5-thread.h.
(com_err_finish_init): New function.
(com_err_initialize): Initialize the new mutex.
* error_table.h: Include k5-thread.h.
(com_err_hook_lock, com_err_finish_init): Declare.

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@16394 dc483132-0cff-0310-8789-dd5450dbe970