Latest pcre-ocaml.7.1.0 breaks mikmatch

constrain version to 7.0.4.  Also forgot dependancy on camlp4.

fixes for pcre-ocaml.7.1.0 pushed upstream so proper fixes shouldn't be
far off.
also constrain older packages to pcre 7.0.4
Merge pull request #2205 from andrewray/mikmatch-pcre7.04

Latest pcre-ocaml.7.1.0 breaks mikmatch