Upgrade to listen 2.0.
Partially work around guard/listen#146.
make sass work with listen >= 1.1.0  < 2.2
cleanup and commenting
extend support to Listen ~>2.4
Re-bundle vendor/listen.

This opens the door for supporting recent versions of listen without
causing undue pain for users of Ruby 1.8.7 on Mac OS X. Listen
versions beyond 1.1 don't support Ruby 1.8.7, but this is installed by
default on many versions of OS X. Widening the version constraint on
listen is also unworkable, since RubyGems will try to select the most
recent version even if it's not compatible with the local Ruby
installation.
Merge remote-tracking branch 'twalpole/listen_2'

Conflicts:
	lib/sass/plugin/compiler.rb
	sass.gemspec
Update the changelog to accurately describe the listen changes.