prevent name clash between ns module and archive

[mobileink]

It's possible to use the same name for an ns module and an archive containing the ns module:

ocaml_archive( name = "foo", deps = [ ...] )
ocaml_ns( name = "Foo_ns", ns = "foo" ... )

This will likely result in the dreaded "inconsistent assumptions over interface" error.

Proposal: add logic to ocaml_archive to check the name of any ns dependency and at least issue a warning if it matches the archive name. Maybe throw an exception.