tends to happen quite often

(thanks eijebong)

Because it doesn’t work, due to a lot of factors, and we can’t fix them.

happens with whitespace keepalive at least

say it’s for horizontal size

Conflicts:
	src/tabs/muctab.py

And probably some other things that use ListTab.matching_names()

Reduce the number of calls to config.get whenever possible. Yields a
performance improvement of at least 10% for the basic use case of
"receiving a message in the current tab". Logging stuff isn’t free
either, even when the call should be a no-op, so we should try to make
the debug log less verbose.

(bug introduced in 1c9257)

if the error has the same id as a sent message, it will be displayed
    with a cross where there is usually a checkmark (ack), and the
    received error will be appended to the message, in red.
if it does not have a know id, it will be added as another message to
    the conversation, without a nick, and in red.

e.g. /set . notify_messages false would set the option for a section
named after the current tab.

(the command args parser would never parse three args, making /set
unable to set section-specific options)

/set displays its results in the form “option=value”, so allowing the
command to interpret the same format as a valid command is only logical
(and allows quick copy/paste and edit).

also fix a check that would make the handler never trigger…