opam >= 0.9.2 exits doing nothing

[ghost]

With opam 0.9.2 or the latest git version opam seems to exit without failing when trying to install some packages. For example after a fresh opam init, opam install oasis successfully install ocamlfind, ocamlify, type_conv and ocaml-data-notation but then exit with code 0. Calling opam install oasis again produces:

The following actions will be performed:
 - install oasis.0.3.0
 - install ounit.1.1.1
 - install fileutils.0.4.4
 - install ocamlmod.0.0.3
4 to install | 0 to reinstall | 0 to upgrade | 0 to downgrade | 0 to remove
Do you want to continue ? [Y/n] 

But exit immediately with code 0 after pressing enter. Tested on Linux and OSX with ocaml 4.00.1 and 4.01.0dev+short-paths.

[avsm]

I observed this behaviour with @samoht while debugging the new solver, but couldn't reproduce it. On the bright side, at least it didn't erase all my files while exiting.

[samoht]

Two issues here:

• the first one is that ounit.1.1.1 is using oasis: there is a cyclic dependencies so OPAM stops. 932e6b8 should improve the error message.
• the second one is wth OPAM is trying to install ounit.1.1.1 instead of ounit.1.1.2 ? this is because my "clever" slicing algorithm really likes cyclic dependencies as they tend to have much dependencies than others. https://github.com/OCamlPro/opam/commit/efc9dc2d50ba04baed5c229eaa41fcc17ddec619 should fix that.