Use ack for ack.vim
Add ag.vim
Squashed 'bundle/ag.vim/' content from commit b0d5073

git-subtree-dir: bundle/ag.vim
git-subtree-split: b0d50730dbf692168307adef625f1378553730df
Merge commit 'd9be3f852e0d052628668fb57e92a20f0ea66e41' as 'bundle/ag.vim'