Include additional arguments and options to the hg command line

I need to supply an identity file to hg for SSH authentication.  Using an identity file from the CLI is semi hacky so instead of building in the hacks prematurely, I thought it would be better to open up the "opts" parameter in the state itself so I may put the hack into my salt-state tree instead of the salt sourcecode.  This allows the salt maintainers to come up with a better method of distributing private SSH keys. 

modules.hg.py clone function already supports the following:

    salt-call hg.clone /tmp/myrepo ssh://hg@bitbucket.org/myuser/myrepo opts='--ssh "ssh -i /tmp/id_rsa_private_bitbucket"' user=appuser

This pull request allows me to specify this in my state formula like so:

    ssh://hg@bitbucket.org/myuser/myrepo:
      hg.latest:
        - target: /tmp/myrepo
        - rev: tip
        - user: appuser
        - runas: appuser
        - opts: --ssh 'ssh -i /tmp/id_rsa_private_bitbucket'

This isn't the only usecase, this is just my use case.

	modified:   hg.py