Update wal_transfer.py

Modified queue to avoid spammy deprecation warnings that make it past --terse.

/usr/lib/python2.6/site-packages/wal_e/worker/pg/wal_transfer.py:90: DeprecationWarning: Queue(0) now equivalent to Queue(None); if you want a channel, use Channel
Add EvilPlankton as a contributor
Introduce a shim to achieve Channel semantics on different gevents