do its work for SIGINFO. Always install libpthread signal handler
wrapper for SIGINFO even if user SIG_IGN's or SIG_DFL's it.
SIGINFO has a special meaning for libpthread: when LIBPTHREAD_DEBUG
enviroment variable defined it is used for dumping an information
about threads to /tmp/.
Reported by: mi
Reviewed by: deischen
MFC after: 2 weeks