Common Question?

I am using bro version 0.7a48, which ofcourse came with the usual slew of
scripts in /usr/local/share/bro. Bro always complains about the file conn.bro
line 197, which is trying to:

if ( have_FTP && is_ftp_data_conn(c) )

That looks ok to me (have_FTP is set to T), the error is:

982815367.072217 ./conn.bro, line 198 (is_ftp_data_conn): run-time error, value used but not set

If I am suffering from this problem, I assume it is by now a common question
on this list. If so and there are archives or places for 'newbies' to go
please point me there...

One more quick question, what does &redef do? I see it smattered all over but
never mentioned in the docs.