need to relock the associated mutex before running the cancellation
handlers.
This patch ensures that the mutex is reaquired in the above case and
also makes pthread_join and pthread_cond_wait act as cancellation points
as required by the POSIX threads standard.
Based on patch from Joseph Link <joelink@joelink.net>.
CCMAIL: 81297-done@bugs.kde.org
git-svn-id: svn://svn.valgrind.org/valgrind/trunk@2409