Unset ctrlp_user_command prior to redefinition
Fix for iTerm themes install on Mavericks

Mavericks cache preferences and overwrites defaults from cache, not
installing it properly. Reading it after install updates the cache with
new values.
Merge pull request #499 from giorni/iterm-plist

Fix for iTerm themes install on Mavericks
Merge pull request #498 from blackxored/ctrlp-unlet

Unset ctrlp_user_command prior to redefinition.