check if kext is present before attempting unload

this is intended to address #1941
Add DownloadStrategy and Cask::Headers for custom :headers support
accepts a :user_agent argument and/or multiple :cookies
  headers :user_agent => 'Netscape/1.0', :cookies => { :cookey => "r00t" }

Also adds a standalone :fake_user_agent for a default UserAgent (Chrome)
  fake_user_agent
References #1175, #958
Adding a cask for the mail plugin MailFollowUp

The installer comes with an uninstaller app (an Automator Workflow at
heart), but I wasn't able to run that with 'script' so I set the
uninstall to manually delete the plugin folder.
services support
Added Cask for Spring Tool Suite (STS).
Merge pull request #1944 from jonahoffline/add_headers_download_strategy

Add DownloadStrategy with custom :headers support
Add FastScripts
Add Zipeg
Merge pull request #2093 from mAAdhaTTah/zipeg

Add Zipeg
Merge pull request #2092 from Cottser/fastscripts

Add FastScripts
SourceTree 1.8.0.3
Merge pull request #2094 from ahbeng/sourcetree

SourceTree 1.8.0.3
HoRNDIS 5
ControllerMate 4.7.1
calibre2opds 3.3-246
Merge pull request #2095 from ahbeng/horndis

HoRNDIS 5
Merge pull request #2096 from ahbeng/controllermate

ControllerMate 4.7.1
Merge pull request #2097 from ahbeng/calibre2opds

calibre2opds 3.3-246
DeltaWalker 1.9.9.6
Merge pull request #2098 from ahbeng/deltawalker

DeltaWalker 1.9.9.6