allow multiple depends_on stanzas + refactor

also:
* disallow combining depends_on :macos comparison expressions
* ohai message when depends_on is present
* explicit accessors for :cask and :formula
* simplify some logic and flatten nested conditionals
* reflow incidental doc
DSL: add depends_on :x11
enable depends_on :arch in jaspersoft-studio
enable depends_on :arch in paraview
remove `caveats` / `x11_required`
enable Snow Leopard compatible version
Add Playlist Assist.app version 1.2.1

Playlist Assist is a floating window to which tracks from iTunes can be dragged and then sorted, arranged, auditioned, edited, exported as text, and saved back to iTunes as a new playlist.
Add Dupin.app version 2.8.2

Now there's Dupin. Your iTunes duplicates manager.
Add Join Together.app version 7.2.0

Join Together will create and export a single AAC or ALAC audio file from the audio data of tracks dragged from iTunes or files dragged from the Finder.
Update filebot.rb

Release FileBot 4.5.3
Add M3Unify version 1.1.1

Stuff a thumb-drive with songs from your iTunes library.
Merge pull request #7872 from bashu/scroll-reverser-legacy

Scroll Reverse and Snow Leopard compatible version
Merge pull request #7886 from vinkla/join-together

Add Join Together.app version 7.2.0
Merge pull request #7892 from vinkla/m3unify

Add M3Unify version 1.1.1
Merge pull request #7891 from rednoah/patch-4

Update filebot.rb
Merge pull request #7889 from vinkla/playlist-assist

Add Playlist Assist.app version 1.2.1
Merge pull request #7887 from vinkla/dupin

Add Dupin.app version 2.8.2
Merge pull request #7845 from rolandwalker/depends_on_x11

DSL: add `depends_on :x11`, permit multiple `depends_on` stanzas
Merge pull request #7846 from rolandwalker/enable_depends_on_arch

Enable `depends_on :arch` in 2 Casks
Merge pull request #7848 from rolandwalker/remove_x11_required

remove `caveats` / `x11_required`