Move the POSIX reg* implementations into the ap_* namespace;

internalise the ap_reg*<->PCRE wrapper:

* configure.in: Add srclib/pcre to the include path.

* include/ap_regex.h: Renamed from include/pcreposix.h.  Prefix all
constants with AP_; prefix all functions and types with ap_.  Define
AP_DECLARE to nothing if necessary.  Remove regcomp error codes.

* include/httpd.h: Include ap_regex.h not pcreposix.h.
(ap_pregcomp, ap_regexec, ap_regfree): s/regex_t/ap_regex_t/.
(ap_regexec, ap_regerror): Prototypes moved to ap_regex.h.

* server/util.c (regex_cleanup, ap_pregcomp, ap_pregsub, ap_pregfree):
Adjust for ap_ prefixed types.  (ap_regexec, ap_regerror): Removed.

* server/Makefile.in: Build util_pcre.c.

* server/util_pcre.c: Copied from srclib/pcre/pcreposix.c; remove use
of PCRE-internals to do error mapping; rename types to add AP_/ap_
prefixes as above.  Use APR includes.  (ap_regerror): Use apr_snprintf.

* srclib/pcre/Makefile.in: Don't build pcreposix.c into libpcre.la.

* modules/*: Update to u...