Fix LaTeX oversight.

Doc/lib/libsgmllib.tex

@@ -102,7 +102,7 @@ Double quotes and backslashes in the \var{value} have been interpreted,
 as well as known character references and known entity references
 terminated by a semicolon (normally, entity references can be terminated
 by any non-alphanumerical character, but this would break the very
-common case of \code{<A HREF="url?spam=1&eggs=2">} when \code{eggs}
+common case of \code{<A HREF="url?spam=1\&eggs=2">} when \code{eggs}
 is a valid entity name).
 
 For instance, for the tag \code{<A HREF="http://www.cwi.nl/">}, this