Added travis.yml file

Added travis file, and finally make tests code non-dependant of the mercurial configuration.
Mercurial packages are taken from the "oficial" PPA of mercurial Ubuntu packagers: https://launchpad.net/~mercurial-ppa/+archive/ubuntu/releases
libgit2 packages for travis are taken from this backports repository: https://launchpad.net/~kronoss/+archive/ubuntu/libgit2