Clean environment for test runs and jetpack script
Make spec suite more resilient to dirty checkout
Fix web specs

- Rack spec was running on commonly occupied ports
- Web spec was angry about debug messages on stderr
Check for jruby, not just ruby
Actually run reloading spec

File extensions. Yep.
Disable failing parts of reloading spec

cc @sul3n3t looking at the original PR
(https://github.com/square/jetpack/pull/33) I strongly suspect that
these tests never actually ran. Let's take a look when you have a chance
and make sure the desired behavior is tested.
Add Travis CI
Simplify script/ci to work with Travis CI
Invoke rake correctly

Invoking `bin/rake` directly only works if your environment is set up to
use the correct ruby. Otherwise, we should use the right ruby explicitly
with `bin/ruby bin/rake`.
Rake must be in the Gemfile to build a binstub