Transport._redirect_to doesn't support 'possible_transports'

[John A Meinel]

I was poking around the import_package code, and part of that code uses the Transport infrastructure to download the various debian files (.dsc, .diff.gz, etc)
It starts by trying to download from the "launchpad.net" url, which ends up redirected to "launchpadlib.net". However, the redirection code doesn't allow tracking 'possible_transports'. Which means that the second connection is always established fresh, rather than re-using the previous connection.

I imagine this doesn't add up to a huge amount of time, but it took a while to track down why I was seeing a 'connect()' for every request, even after passing 'get_transport(base, possible_transports=...)'.

The code I would like is "_redirected_to(..., possible_transports=...)" which would then pass that to its own 'get_transport()' call.