update sketchup to v2014 and add sketchupviewer

sketchup has 3 products, make, pro and viewer
see http://www.sketchup.com/download/all
update to latest 2014 version
add sketchupviewer
pro will be added to versions repo
Add Coq IDE, version 8.4pl4
Merge pull request #5090 from jconley/sketchup

update sketchup to v2014 and add sketchupviewer
Merge pull request #5124 from vitorgalvao/fix-5123

Add Coq IDE, version 8.4pl4
add scratch cask
upgrade darktable to v1.4.2
add luminance-hdr 2.4.0
Merge pull request #5126 from jconley/scratch

add scratch cask
Merge pull request #5128 from vitorgalvao/fix-5127

upgrade darktable to v1.4.2
Update Zotero to 4.0.21.5

Value of `version` stanza now reused in `url`, ref. #4910.
Merge pull request #5129 from ndr-qef/zotero

Update Zotero to 4.0.21.5
install rspec; move first few tests over

refs #5080
Merge pull request #5120 from caskroom/install-rspec

install rspec; move first few tests over
Add Cask Xamarin, replacing older Xamarin Casks

These packages are: xamarin-android, xamarin-ios, and xamarin-studio.
They have been added to homebrew-versions.

Only call caveats once on Xamarin cask
rspecify scopes and download strategy tests

refs #5080
Merge pull request #5132 from caskroom/rspecify-part-1

rspecify scopes and download strategy tests
Merge pull request #5118 from fapper/xamarin

Add Cask Xamarin, replacing older Xamarin Casks
Merge pull request #5125 from jconley/luminance-hdr

add luminance-hdr 2.4.0
Seil 10.9.0
Merge pull request #5134 from NanoXD/seil

Seil 10.9.0