small watch improvements and unit tests

[matthewmeyer]

• Adding basic unit tests for watch mode
• Forward date the packhost modified time stamp 10 seconds to keep the watcher from going crazy, see: https://github.com/webpack/watchpack/issues/25
• Improved the watch mode logging to make it easier see rebuilds occuring

[matthewmeyer]

Looks like debug is enabled and going to stderr which is a failure condition in my test. Can I change the debug config to stdout?

[christopheranderson]

Yeah, that's fine. It's not intentionally going to stderr, just default config.