regex: Add ap_regexec_ex() which can take a starting offset to match from.

regex: Add ap_regexec_ex() which can take a starting offset to match from.

* include/ap_mmn.h:
  Bump MMN minor.

* include/ap_regex.h:
  Declare ap_regexec_ex().

* server/util_pcre.c(ap_regexec, ap_regexec_len, ap_regexec_ex):
  Reuse existing ap_regexec_len() code to implement ap_regexec_ex() where the
  offset is given instead of zero, then implement ap_regexec{,len}() in terms
  of ap_regexec_ex().

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1915267 13f79535-47bb-0310-9956-ffa450edef68