check if kext is present before attempting unload

this is intended to address #1941
safer test for currently running app

The previous version could fail if the specified bundle was not installed.
Here we tell "System Events" until determining it is safe to do otherwise.
add caveats for Little Snitch

note - this currently is the only app cask that does not have
a "link" or "install" stanza
flag handling consistent btw install/uninstall

This makes uninstall process flag arguments in the same manner
as install. Any argument with a leading dash is assumed to be a
flag, not a Cask.  Argument processing still needs work, unknown
flags and spelling errors are silently accepted.
Downloads the driver from the manufacturer's homepage.
Make caskroom configurable via command line argument
Clearer instructions for options
Updates textexpander cask to version 4.2
Merge pull request #2067 from farfanoide/update-textexpander

Updates textexpander cask to version 4.2
RStudio 0.98.490
Merge pull request #2068 from jglenes/rstudio-490

RStudio 0.98.490
Added test for custom --caskroom argument
Merge pull request #2061 from Aigeruth/prolific-usb-serial-driver

Downloads the driver from the manufacturer's homepage.
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
xScope 3.6.3
Merge pull request #2070 from ahbeng/xscope

xScope 3.6.3
Add support for colorpicker type
Refactor similar method structure in dirs and files into one for re-use.
By using the name of the method calling fs_command we remove duplication
Ukelele 2.2.6
Merge pull request #2073 from SebastianZaha/ukelele

Ukelele 2.2.6