Tweak description of PortableUnixMailbox: "From " lines are actually

gward · gward · commit 02669a35bc30 · 2002-09-23T19:32:42.000Z
quoted (or mangled) *at* delivery-time, not "well before" it.  (At least
that's how Exim and qmail work.)
diff --git a/Doc/lib/libmailbox.tex b/Doc/lib/libmailbox.tex
@@ -45,7 +45,7 @@ \section{\module{mailbox} ---
 ``\var{name} \var{time}'' portion of the From line is ignored, to
 protect against some variations that are observed in practice.  This
 works since lines in the message which begin with \code{'From '} are
-quoted by mail handling software well before delivery.
+quoted by mail handling software at delivery-time.
 \end{classdesc}
 
 \begin{classdesc}{MmdfMailbox}{fp\optional{, factory}}
