Added condition to make sure the message being sent out to the channel is not a retweet, and was sent by one of the two twitter accounts being followed by the plugin.
Merge pull request #3 from phildowney/master

Basic Tweet Validation
- Pulling into master branch.
- This code will be enhanced later.
- Updated Twitter plugin; additional twitter users can be followed with !follow <twitter username>
- Fixed some code style issues.
- Added more friendly messaging when trying to follow a Twitter user fails.
- Reduced message delay to 250ms to speed up multi-line messages.
- Fixed example configuration file.