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
Add some checks that the Channel shim chooses gevent.queue.Channel

Previously, there was no checks to make sure that gevent.queue.Channel
was used when possible.
Fix channel shim test for gevent 1.0.0

Gevent 1.0 specifies this as its version, not 1.0.0, breaking the
comparison spuriously if one has version 1.0 installed exactly.
Remove redundant conditional
Use s3-external-1 endpoint for us-standard

This is the endpoint in us-east-1, where most instances are.  This is
not being applied to the v0.6 maintenance releases to avoid changing
behavior for those who are closer to Seattle.
Elide other backends besides S3 in requirements.txt

It's not clear how to make things cleanly optional but not a usability
nightmare (e.g. installing *no* backends by default for 'pip install'
based people) within the Python packaging framework, so don't try..for
now.
Avoid deleting keys that have a new-ish timestamp

This is a paranoid safeguard against mess-ups; even if turned against
the wrong prefix it is likely many backups will be retained.

Some of the tests need adjustmenmts to not freak out about this
safeguard.
Increase socket timeout to deal with pathological cross-region issues