Added OSX desktop notifications using terminal-notifier

Requires Xcode
WIP - No configure.ac changes
Log message when cannot send desktop nofication
Added configure checks to enable desktop notifications on OSX
Added libgcrypt-devel to cygwin dependencies
Removed gcc linking from cygwin install
Fixed spelling mistake in configure.ac
Merge branch 'osx-notify'
Merge branch 'master' into brew