Zsh: enable hg vcs_info for prompt

Not as useful as the Git info, since we only use lightweight bookmarks
and the branch info always reads "default".

Nevertheless, enabling in case there are ever any updates which make it
better/worthwhile.

Signed-off-by: Wincent Colaiuta <win@wincent.com>
Vim: ignore untracked files in Lawrencium submodule

Keep the noise out of `git status` caused by the untracked file
"doc/tags".

Signed-off-by: Wincent Colaiuta <win@wincent.com>