Publish a message whenever an attribute is changed

lib/live_resource/redis_client/attributes.rb:
  RedisClient#attribute_write will now perform a Redis 'publish'
  if the value is being changed.  The channel is the key that is
  being changed (e.g. "foo_class.bar_name.attributes.color").  The
  value is the new attribute serialized value.

test/attribute_test.rb:
  Add a unit test to make sure a message is published if and only if
  an attribute is changed.

test/test_helper.rb:
Rakefile
  Add a mocha development dependency.  It's more straight forward to
  unit test this new functionality with mocha.