fix for ocaml 4.01 / split META-file

1) recent OCamlMakefile
2) fix for ocaml 4.01beta
3) Split the META file in two sections:

* one section for preprocessor 'mikmatch_pcre' (canonical way would be mikmatch_pcre.syntax, but this would break existing makefiles)
* one for the runtime part 'mikmatch_pcre.lib'

One section, that you can pass to ocamlfind for linking; one section for preprocessing.  This simplifies build instructions, if you use different (incompatible) camlp4-extensions.