Fixing vows executable clusterfuck

* Explicit executable override is still available
* Moving `vows` from a devDep. to a regular dep. as it should have been from
the get-go.
* Using `node_modules/grunt-vows/nodule_modules/vows/vin/vows` executable when
used as a dependency for your project
* Using `node_modules/vows/bin/vows` when this task tests itself (testception?)
* Adding more files to .npmignore. Leanness ftw!
* Verbose-log the command which grunt-vows executes for each target