bundle now does handle names, urls and tars via cache.add.
if the package is a directory only the package.json is read.
this makes bundling faster and fixes a bug with cache.add where
the bundling cache was added recursively.
* also fixed a bug with package names eg vows@0.5.1
* bundle does not support version ranges eg sax@">=0.1.0 <0.2.0"
* now throws an error if bundling packages without dependencies