This reverts commit 2fba646837.
PCRE-8.39 throws weird valgrind backtraces on some systems, see
http://news.php.net/php.cvs/93494 . Those could be false positives
due to some changes in JIT, still i couldn't 100% ensure this.
Thus, better we continue to ship 8.38 bundled for now, and apply
patches, if needed.