Reverted e86de36 - Reuse a single connection when doing a bucket list

We need a more generic approach to connection pooling.
Reuse HTTP connections

Revived very old approach from v0.9.9-speedup branch (149226b)
TODO: Proxies not supported!
Add proxy support
Merge branch 'http-speedup'
Merge branch 'master' of ssh://github.com/s3tools/s3cmd