Updated references from Rev to Coolio.

[fengi]

Tests are passing under mri 1.8.7 and 1.9.2, but I didn't actually use it under anything else then 1.9.2 yet.

Besides I made the require in watchr.gemspec explicitly relative to get it to build under ruby 1.9.
Though I hope there's a better way to do this.

[mynyml]

Love the patch, but it breaks backwards compatibility. Probably needs both rev and coolio for now, with a deprecation notice when running with rev.