NULLify the destructor field when a thread key is deleted.  This
allegedly fixes the following (haven't tested it myself):

valgrind: vg_scheduler.c:3454 (scheduler_sanity): Assertion
`vg_thread_keys[i].destructor == ((void *)0)' failed.


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@1356 a5019735-40e9-0310-863c-91ae7b9d1cf9
1 file changed