More efficient listing of installed Casks

[hanxue]

Fix for #911

[hanxue]

Replace older pull request #1416 due to changes from a1fa264

Need opinion and assistance from @phinze :

1. Listing the content of Caskroom is significantly faster.

Using existing code puts_columns Cask::CLI.nice_listing(Cask.installed) it takes 0.5 seconds on my machine

$ time brew cask list
caffeine        jd-gui      macupdate-desktop   spotifree
chicken         jdownloader     nosleep         spotify
colloquy        jitsi       oovoo           transmission
diffmerge       lastfm      picasa          vagrant
dradio          lastpass-universal  rdio
haskell-platform    litecoin        retroshare

real    0m0.507s
user    0m0.438s
sys 0m0.067s

Simply listing the contents of Caskroom system "ls", "/opt/homebrew-cask/Caskroom" takes 0.1 seconds

$ time brew cask list
alfred          jd-gui          opera-next
bluestacks      jdownloader     picasa
caffeine        jitsi           privoxy
chicken         kdiff3          rdio
cocktail        lastfm          remotebox
cocktail-mavericks  lastpass-universal  retroshare
colloquy        lime-chat       spotifree
deeper          lion-disk-maker     spotify
diffmerge       litecoin        squidman
dradio          macpilot        sublime-text-dev
growl-fork      macupdate-desktop   tinkertool
haskell-platform    mnpp            transmission
intellij13beta      nosleep         vagrant
itweakx         onyx
itweax          oovoo

real    0m0.114s
user    0m0.078s
sys 0m0.035s

1. Using the directory listing approach, the first test will not work https://github.com/phinze/homebrew-cask/blob/master/test/cask/cli/list_test.rb?source=cc

Does it make sense to make the test run

 it 'lists the installed casks in a pretty fashion' do
    lambda {
      Cask::CLI::List.run
    }.must_output puts_columns Cask::CLI.nice_listing(Cask.installed)`

?

[fanquake]

If you think that tests need to be updated/removed, you should include those commits in this pull.

[muescha]

since app names and filenames can be different i dont like this hack.

i would prefer a more detailed listing with file name, app name, description ( #1790 )

[phinze]

I'm working on new code around brew list that will address this issue - it will also properly list casks that have been installed then renamed. I'll close this once that code is pushed.

[phinze]

Okay modified brew list has landed so closing this guy. Thanks for helping push this functionality forward! 🍴