req_header implementation ...

I've just committed a cleanup to the ACLHTTPHeaderData source : it had a
complete copy of ACLRegexData embedded in it, which was not needed.

There was another glitch - the source files had been copied, but the
#include guards had not been updated to reflect the new header file
name.

I think guido wrote this? Anyhow, the general rule should apply to
anyone - if you copy code, try to find a way to not end up with
duplicate identical code - which is what had happened in this case.

I don't know if my fixed code works correctly or not - I think it does -
because there are no unit tests for the new feature.

Cheers,
Rob