Does not support resource with FTP URL-s

[Chealer]

Disclaimer: I did not verify this issue (I assume a change equivalent to one made for pip had a result equivalent to the one for pip).

DataPusher 0.0.6 supported loading resources over FTP. However, this seems to be no longer the case starting from 0.0.13, after commit 4610197, which stopped DataPusher from using urllib2 to use the "Requests: HTTP for Humans" library, which - unsurprisingly - only supports HTTP, as it is based on urllib3, which - despite its name - does not support FTP like urllib2 did.

I'm filing this to document the change but also so that the code can be cleaned up. The error message for unsupported schemes ("Only http, https, and ftp resources may be fetched.") has not changed and suggests that FTP resources are still supported.

Note that DataPusher's alternative xloader does not support FTP any more.