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
use "staged" instead of "installed" for Caskroom

refs: #6783
use installer :manual in adobe-creative-cloud
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use installer :manual in baiduinput
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use installer :manual in default-folder-x
use installer :manual in google-nik-collection
use installer :manual in jdownloader
use installer :manual in little-snitch
use installer :manual in logmein-hamachi
use installer :manual in paye-tools
use installer :manual in ps3-media-server
use installer :manual in scout
use installer :manual in sogouinput
use installer :manual in sts
use installer :manual in thinkorswim
use installer :manual in titanium-studio
use installer :manual in utorrent
use installer :manual in vlc-remote