Replace PCRE with PCRE2 where it is available.

Replace PCRE with PCRE2 where it is available.

This patch removes the needless assignment of re_erroffset in the conf pool
by the worker threads; such mistakes break the shared copy-on-write pages of
memory that should have remained common between all httpd worker processes.

Two de-optimizations are inherent in this patch, the former ovector-on-stack
opportunity is lost unless implemented as a new general context. Safer that
we either create a new general context using pool allocation, or recycle a
per pool or per thread match_data buffer of some arbitrary 10 elts or so.

Submitted by: wrowe, Petr Pisar <ppisar@redhat.com>

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1773454 13f79535-47bb-0310-9956-ffa450edef68