Replace Ack with the Silver Searcher (ag)

This is simply a 'swap one for the other' topic branch. If we
collectively believe ag to be better perhaps we will want to have
everyone default to it vs ack. It requires users to install ag before
the plugin will work but the same is true for Ack on certain machines as
well.

I'll issue a pull request for team review but suspect we'll probably
just leave the topic branch for now and let folks merge their own
version of what tools they like. You can also manually install via
vundle and remap the ack commands in your personal config as well. This
is what I have been doing but feel like others would benefit from this
being in the core distro.
Go ahead and BundleInstall as part of the rake task.
Add missing gist-vim dependency
Merge pull request #12 from neo/fix_gistvim_dependency

Fix gistvim dependency
Added map to open gem file by typing gm
Merge branch 'master' of github.com:bakis2011/vim-config
Merge pull request #14 from bakis2011/master

Added shortcut 'gm' for opening the Gemfile
Merge pull request #10 from neo/ag

Replace Ack with the Silver Searcher (ag)
Merge pull request #11 from seanknox/bundleinstall_from_cli

Go ahead and BundleInstall as part of the rake task.
Add back g* for Silver Searcher
Merge branch 'master' of git://github.com/neo/vim-config into upstream_merge

Conflicts:
	.vim/common_config/plugin_config.vim
	Rakefile