Remove all \bcode / \ecode cruft; this is no longer needed.  See previous
checkin of myformat.sty.

Change "\renewcommand{\indexsubitem}{(...)}" to "\setindexsubitem{(...)}"
everywhere.

Some other minor nits that I happened to come across.
diff --git a/Doc/lib/libmimify.tex b/Doc/lib/libmimify.tex
index 171e7d2..2982755 100644
--- a/Doc/lib/libmimify.tex
+++ b/Doc/lib/libmimify.tex
@@ -1,6 +1,6 @@
 \section{Standard Module \sectcode{mimify}}
 \stmodindex{mimify}
-\renewcommand{\indexsubitem}{(in module mimify)}
+\setindexsubitem{(in module mimify)}
 
 The mimify module defines two functions to convert mail messages to
 and from MIME format.  The mail message can be either a simple message