recast method `destination_path` as `staged_path`

* part of DSL 1.0 review
* `destination_path` was always a bit vague (it refers to
  Cask-specific, version-specific location under
  `/opt/homebrew-cask/Caskroom`)
* here renamed `staged_path` to match upcoming command verb
  `brew cask stage`
* rename also intended to reduce confusion when we implement
  copying as a configurable alternative to symlinking
* transitional `destination_path` methods to remain while
  Casks are converted (this was documented as a part of the
  DSL, and used by 39 Casks in main repo)
* unrelated variables containing "stage" recast for clarity
reuse version in boom-recorder.rb
reuse version in fliquo.rb
reuse version in geneious.rb
reuse version in jabber-video.rb
reuse version in preform.rb
reuse version in sauerbraten.rb
reuse version in slender.rb
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
Upgrade DeathToDSStore.app to v1.0.4
Upgrade MacPorts to v2.3.2 and add Yosemite support
Merge pull request #6828 from fenhl/patch-1

Upgrade DeathToDSStore.app to v1.0.4
Merge pull request #6829 from diimdeep/macports

Upgrade MacPorts to v2.3.2 and add Yosemite support
Merge pull request #6785 from rolandwalker/reuse_versions

Reuse version number in 7 Caks
Merge pull request #6783 from rolandwalker/rename_destination_path

recast method `destination_path` as `staged_path`
Add MagicPrefs Latest

Added MagicPrefs Cask, it uses the latest version available
Merge pull request #6826 from andres-torres-marroquin/magicprefs

Add MagicPrefs Latest
updated Aerofs to 0.8.67
Merge pull request #6832 from vitorgalvao/fix-6819

updated Aerofs to 0.8.67
Added cask for Laplock