Add camlp4 packages.

The 4.02 package installs the latest sources from git (to be replaced
with a stable tarball when released).

Earlier revisions are just a dummy package since they were present
in the base install.

Discussed with @samoht
camlp4: correct the git branch to trunk
Merge pull request #1970 from avsm/master

Add camlp4 packages.