r5080 didn't go far enough -- since 0.58, anyone on Unix who didn't previously

have default settings for "bell overload" mode will have inherited a twitchy
set of defaults where bells are disabled after 2ms and enabled after 5ms,
rather than 2s and 5s as intended. This error has probably propagated into some
people's saved sessions by now, but there's not much to be done.

git-svn-id: svn://svn.tartarus.org/sgt/putty@8389 cda61777-01e9-0310-a592-d414129be87e