This renames all the existing API methods, to use a consistent
"d=get_XYZ()" (for Deferred mode) or "dg.wormhole_got_XYZ()" (for Delegated
mode). It updates cmd_send/cmd_receive/cmd_ssh to use the new API.
Since we now have get_welcome(), apps handle the Welcome message with a
Deferred callback instead of registering a "welcome handler". This lets us
make sure we've finished printing any server message-of-the-day or "you
should update your client" message to stdout before using stdio to ask for
the wormhole code. (Previously, the code-input prompt was overwritten by the
server message, and it was ugly). refs #145. This approach adds an extra
roundtrip to the receiver, but we can fix that (see #145 for details).
Because of that change, the server-is-being-slow message is printed at a
slightly different time, so those tests needed some extra work to exercise it
properly.
The Welcome class prints a message if the server recommends a CLI version
that's newer than what the client is currently using, but only if the client
is running a "release" version, not a "local" development one. "local"
versions have a "+" in them (at least when Versioneer creates it), but
Welcome was looking for "-" as an indicator. So it was printing the warning
when it shouldn't be.
