v.12 Fixed regression involving buffer reassociation on forced renicks.
In so doing, made behavior slightly more aggressive. Also fixed problem
persisting local-module modes across reconnects.

WRT the latter, if you were to toggle off a local module, like
`erc-sasl-mode', and reconnect, ERC would activate it again the second
time through. (Though fixed, this needs an accompanying test.)

Also spotted:

  *** irc.foonet.org 900 * * tester You are now logged in as tester
  *** irc.foonet.org 903 * Authentication successful

Pretty redundant/noisy. We should maybe add a catalog entry for 903 and
a handler for 900 (although some servers use 900 for non-SASL purposes,
I believe).

Another possible UX annoyance is that local toggles, like
`erc-sasl-mode', don't currently work in target buffers at all. We
should maybe wrap them in an `erc-with-server-buffer'.