- use propagatedBuildInputs to make sure ocaml plugin stuff is in path
- updated coqPackage.heq (broken url)
- fixed use of `DESTDIR` and `COQMF_COQLIB` in mkCoqDerivation
- adding `COQCORELIB` environement variable to put ocaml plugin files in the right place
- make metaFetch available from `coqPackages`
* compcert: preparation to move in coqPackages
* compcert: move into coqPackages
* compcert: remove version 3.7
As a consequence, also remove VST version 2.6
These were broken.
Vincent Laporte