packages with optional dependencies require multiple packages

[jedahan]

hammer.js has an additional file jquery.hammer.js that is optional. For now, publishing 'hammer.js' and 'hammer-jquery' will have to be the workaround. This might be better handled in CommonJS first.

[caolan]

Note: this might be addressed with an optionalDependencies property in package.json (which will display a message on installation similar to pacman's handling of optional deps) and virtual packages which would allow both hammer-standalone and hammer-jquery to satisfy the 'hammer' virtual package for dependants.