I believe that it is best to have two different time formats for
logfiles and normal rcirc buffers.  Logfiles need additional precision,
specifically the date and maybe the time zone, while normal buffers do
not.

The patch adds a single variable, rcirc-log-time-format, to control the
time format in logfiles, which is done by replacing the usage of
rcirc-time-format in rcirc-log with it.

I figured "%F %T %z " was a sensible default, although feel free to
change it as you wish.