ap_regex: PCRE needs buffers sized against the number of captures only.

ap_regex: PCRE needs buffers sized against the number of captures only.

No more (useless), no less (or PCRE will allocate a new buffer by itself to
satisfy the needs), so we should base our buffer size solely on the number
of captures in the regex (determined at compile time from the pattern).

The nmatch provided by the user is used to fill in pmatch only (up to that),
but "our" buffers are sized exactly as needed to avoid oversized allocations
or PCRE allocating by itself.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1897244 13f79535-47bb-0310-9956-ffa450edef68