Add $GOPATH
Fix typo in the Vundle URL
Add the Go vim plugins in a rather roundabout way:

* Add new Pathogen install script so we have Pathogen again if we need
  it.
* Add symlink from brew-installed Go vim plugins to new special-case
  Pathgoen-infected path
* Load only this special path with Pathogen, leave everything else to
  Vundle