tevent: version 0.9.28

tevent: version 0.9.28

* Fix memory leak when old signal action restored (bug #11742)

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

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>
Autobuild-User(master): Stefan Metzmacher <metze@samba.org>
Autobuild-Date(master): Fri Feb 19 19:12:25 CET 2016 on sn-devel-144

(cherry picked from commit da74d0c317be9ce67eb5d00d232167d466f68a1e)

The last 12 patches addressed bug #11771:
Backport tevent-0.9.28.