Merge pull request #12 from Chris00/master

Locate "topfind" when using opam "system" compiler.
Support pure interface modules in libraries.

This commit allows an mli-file to implement a module listed in the Modules
field of a library, provided that it only includes type and signature
definitions.  The mli- and cmi-files will be installed along with the
library.
Merge pull request #13 from paurkedal/InterfaceModules-3

Support pure interface modules in libraries.
Merge branch 'master' of git://github.com/ocaml/oasis
Add a Maintainers field in _oasis.