updating the coq package

[Ralf Treinen <treinen@free.fr>]

Hello,

I have been working on updating the coq package. The current state is
on the experimental/master branch. The packaging neeeds some serious
review since I am not a coq user. In particular, I have updated to
the latest upstream release (8.10.2) and re-activated building of the
coqide package, now based on lablgtk3.

Particular problems:
- tests have to be adjusted. Currently I get test failures the origin of
  which I haven't tracked down yet, so I can only build with
  DEB_BUILD_OPTS=nocheck. This obviously has to be fixed.
- When building the package with coqlib installed, dh-ocaml generates
  dependencies both on the installed version of coqlib, and the one
  being compiled. The current workaround is a build-conflict, which
  does the job but is annoying. I suspect that the root of this
  is a wrong setting of a searchpath in one of the makefiles which gives
  priority to libraries installed by the system.

The package has to go through NEW since there is a new coqide package. Any
takers for the review ?

Cheers -Ralf.