Support for internal endpoints in cloudfiles

Sorry for the ugliness of the commit history. I didn't do this cleanly from the start. The diff is clean, however.

Being able to use the internal network endpoint gives significant speed improvements (upwards of a whole second from my brief benchmarking) when your application server and cloudfiles are in the same region/datacenter.

RE: https://github.com/apache/libcloud/pull/186#issuecomment-33209925