VLC 2.1.4
Merge pull request #3088 from ahbeng/vlc

VLC 2.1.4
add generic interface for determining installed version of apps

New in cask:

update_version - version to compare against on update check. Is same as
`version`, must be set for `latest` apps. Not used atm.

check_version_cmd - commands to run inside installed app dir to get the
version out. Maybe parse a plist or run a `bin --version`.
modify firefox cask to check for version on info
cache installed version, display msg if update available
fix version comparison
remove trailing white spaces in info output