Move the functionality from filter_threadnums into filter_stderr, so that

Move the functionality from filter_threadnums into filter_stderr, so that
it applies to all tests.  Then remove all references to filter_threadnums.

Also:

* match and transform not only "Thread #n" and "thread #n"
  but also "Thread n" and "thread n", where n is [0-9][0-9]*.

* use -e ... for the sed commands where possible, to reduce the number
  of processes that have to be started

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@8839