Switch to AndroidHttpClient and explicit targeting.
Change MMS network request pattern.

Currently we're flipping the radio in "MMS" mode, and connecting through
any proxies specified in the APN.  This always work, or at least doesn't
seem to work on Sprint, since the configured mms proxy rejects proxy
requests.

Instead we try the following in this order:

1) Connect over normal data connection directly to MMSC.
2) Connect over MMS radio connection to MMSC.
3) Connect over MMS radio connection with any configured proxy to MMSC.

Hopefully this doesn't fuck up shit on other unknown networks.