Test for issue 1239

A test that fails in the current version. See ticket on the forge for more explanations:

https://forge.ocamlcore.org/tracker/index.php?func=detail&aid=1239&group_id=54&atid=291

A couple more details:
In its current state, oasis incorrectly compiles packed libraries, which leads to warnings of the form

```
Warning 31: files src/packedlib.cmo and src/packedlib.cma(Packedlib) both define a module named Packedlib
```
When a library is packed, oasis decides to create an mlpack instead of an mllib. However in the absence of an mllib file, ocamlbuild adds some spurious modules in the cma, and those modules may end up being in several cma, or uselessly added when compiling an executable.