That's not the best patch ever, but that'll fix 'uname -s' when some env variables contain hyphens (which seems to be valid with bash but not with sh).
Unix.open_process_in is hard-coding '/bin/sh', so switch to the more neutral Unix.create_process
Merge branch 'master' of https://github.com/OCamlPro/opam
Manually merge #210
Big refactoring work.
The API is now much cleaner. There are still some work to do to clean-up OpamClient.ml, this can be fixed later.