Subject: document that "all bets are off if the file contains non-unique join fields"

From: [email-masked]
Date: Fri, 19 Aug 2011 04:29:32 +0800

Mention in the join(1) documents that "all bets are off if the file
contains non-unique join fields", e.g.,
a
b
b
c
Also mention if you get this email.