updates to reification.

- pull Std into coq-plugin-utils
- change build procedure to use ocamlfind (major changes to
  Makefile)
- reification and materialization of evars
- eliminate dead Makefile.coq patch
rule to build the plugin.
Specializations of ReifyEnv

- ReifyEnv -> ReifyEnvOption
- New ReifyEnv takes [Term.constr list]