implement in_hg(), hg_get_branch_name(), hg_prompt_info(), and hg_dirty() for the mercurial plugin
named functions similar to subversion plugin, to give theme maintainers an easier life
The -v flag for these commands really isn't very useful. It will
output some information about the hooks it is running, but that is
generally not useful and just noisy. The desire to add -v to these
commands is exceptional and IMHO it's better to make the common
case of not seeing those messages the supported behavior.
