lib: tevent: Fix memory leak reported by Pavel Březina <pbrezina@redhat.com> when...

lib: tevent: Fix memory leak reported by Pavel Březina <pbrezina@redhat.com> when old signal action restored.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=11742
Bug: https://bugzilla.samba.org/show_bug.cgi?id=11771

Signed-off-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>
Autobuild-User(master): Andreas Schneider <asn@cryptomilk.org>
Autobuild-Date(master): Thu Feb 18 01:42:50 CET 2016 on sn-devel-144

(cherry picked from commit 833a2f474367624dd9980abb28227850e95fe976)