Downgrade CaskAlreadyInstalledError to a warning

Automatic installs - like thoughtbot's laptop script - fail when we
use Homebrew's onoe method.  Using opoo (to warn) will let the
scripts complete successfully when they try to install packages that
have already been installed.

Test for downgrading AlreadyInstalledError to warning
re-use version in apptrap
re-use version in camerabag
re-use version in curb
re-use version in cx
re-use version in decitime
re-use version in dupscanub
re-use version in elyse
re-use version in flash-player
re-use version in garmin-communicator
re-use version in iannix
re-use version in ipaql
re-use version in itunesscrobbler
re-use version in kylo
re-use version in lyrics-master
re-use version in metanota
re-use version in password-gorilla
re-use version in programmer-dvorak
re-use version in scansnap-manager
re-use version in smartsynchronize