Tests are run with locally installed coffee

This is good at least for two reasons:
- we can be certain that the tests are run with the coffee version
  specified in `package.json`
- tests can be run even if `coffee` is not installed globally
Apply the same shebang for all shell scripts

Nothing was broken but it's nice to have a "standard" shebang accross
all scripts.

See http://en.wikipedia.org/wiki/Shebang_(Unix)#Portability