Rename Console to Console_unix and Console_xen to ensure they remain distinct

We now need to patch mirage to generate the right Console module as an
alias to Console_unix or Console_xen.

Fixes #25
Merge pull request #26 from avsm/fix-module-clash

Rename Console to Console_unix and Console_xen to ensure they remain distinct
Add missing dependency on mirage-unix to mirage-console.unix
add mirage-unix to opam depends
Merge pull request #27 from avsm/master

Add missing dependency on mirage-unix to mirage-console.unix
-enable-xen only if xen-gnt.unix is installed

xen-gnt.unix is installed only if xenctrl.h is there
Merge pull request #29 from samoht/master

-enable-xen only if xen-gnt.unix is installed
Improve opam

the depopts things are a bit crazy ... we should have virtual packages instead!
Run the tests in the Travis scripts
add the opam black magic to set-up the environment
Merge pull request #30 from samoht/master

Improve opam
Prepare the release