[bug#33811] [PATCH] Opam importer improvements

[Julien Lepiller]

Hi,

here are a few improvements to the opam importer. The first patch is 
somewhat unrelated and moves coq and coq packages away from ocaml.scm to 
a new coq.scm file. The second and third patches add a recursive option 
and an updater for opam, while the fourth and fith patches make sure it 
works for ocaml-graph: I found that the importer didn't support comments 
that are present in the opam file for ocamlgraph.