Vim: add some more Gundo settings

I was looking at an alternative to Gundo which supposedly has more
options and doesn't depend on Python:

  https://github.com/mbbill/undotree

Nevertheless, I need Python anyway (for UltiSnips) and it turns out that
Gundo has a reasonable amount of configurability anyway; see:

  http://sjl.bitbucket.org/gundo.vim/

Let's add some settings!

Signed-off-by: Wincent Colaiuta <win@wincent.com>
Git: improve `git grep`

Add a `git ack` alias that is `git grep` tweaked to look more like Ack,
and add a couple of other settings stolen from:

  http://travisjeffery.com/b/2012/02/search-a-git-repo-like-a-ninja/

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

With some new acquisitions, and additional switches for Git.

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