Replace mime library.

Hello. This is the same PR as in #87 with 2 differences:

- Only replace the mime library (not upgrading dependencies)
- Use "node 0.8-friendly" dependency declarations (as requested in that PR).

So, more or less the same PR, but since there was no activity there, I rather just took the matter into my own hands. Also because this currently breaks browserify support for request (see request/request#455)