Propose a mechanism to auto-remove temp files on response close/finish

Add a second option to "multipart({}, true);" to trigger automatic temp files deletion.

It's a proposition and maybe the implementation is not totally compliant with Connect/Node standards.

I also wasn't able to run the repo tests (Uncaught Error: connect EADDRNOTAVAIL).
This module should not write to stdout or stderr. We need to instead find a way to expose the error or swallow it.