[PATCH] lib/tevent: fix race with signals and tevent_common_add_signal

[tridge at samba.org]

 > We carefully preserve the old signal handler, but we replace it before
 > we've set up everything; in particular, if we fail setting up the
 > pipe_hack we could write a NUL char to stdout (fd 0), instead of
 > calling the old signal handler.
 > 
 > Replace the signal handler as the very last thing we do.

applied, thanks!