Update vim-improvements.vundle

This removes a redundant Bundle that already appears on line 9. This was throwing warnings for me whenever I started macvim.
Merge pull request #470 from martco/patch-1

Update vim-improvements.vundle
Decided disabling arrow keys was hurting new people too much
Remove duplicated plugin
Fix Ag functions

I believe this is what is intended? It was not working for me like it was...
Merge pull request #474 from lfilho/patch-1

Fix Ag functions