Work around a LaTeX2HTML bug that caused the "m" in "mutable" to be dropped

in one place.

Doc/ref/ref3.tex

@@ -380,7 +380,7 @@ comparison: if two numbers compare equal (e.g., \code{1} and
 \code{1.0}) then they can be used interchangeably to index the same
 dictionary entry.
 
-Dictionaries are \obindex{mutable}mutable; they are created by the
+Dictionaries are mutable; they are created by the
 \code{\{...\}} notation (see section \ref{dict}, ``Dictionary
 Displays'').