[MERGE][1.2][#185394] Disconnect and reconnect the smart medium after getting "unknown method" error from server if a request body was sent.

[Martin Pool]

Martin Pool has voted tweak.
Status is now: Conditionally approved
Comment:
My biggest concern is the disruption to users who enter their password 
on
every reconnection.  So I think we should at least give them a message
explaining what is happening and why.  Something like:

   Server is too old for streaming push, reconnecting...

And I would say the NEWS entry should be right at the top in the "notes
when upgrading", and explain that this might require you to reenter a
password or passphrase.

If this is 1.2 it will make deployment of 1.2 onto Launchpad urgent; it
really should be there before 1.2final.

+        # Be optimistic: we assume the remote end can accept new remote
+        # requests until we get an error saying otherwise.  (1.2 adds 
some
+        # requests that send bodies, which confuses older servers.)
+        self._remote_is_at_least_1_2 = True

It might be more accurate as a ternary None/True/False, but it's 
probably
not worth it.

The fact that we have to do this here indicates to me the value of 
having
a machine-parseable indicator of the version in messages, even though
we'll generally try to avoid making decisions based on it.  Not to
mention having the body explicitly marked.  So we should try to get on
with doing the protocol 3 changes, and make sure that they consider how
we detect protocol version.


For details, see: 
http://bundlebuggy.aaronbentley.com/request/%3C20080206060316.GB5911%40steerpike.home.puzzling.org%3E