htmlxref.cnf: new URLs for the MIT-Scheme manuals

[Thérèse Godefroy]

Hello,

The links to all 4 MIT-Scheme manuals have changed. Here is the diff:

--- htmlxref.cnf
+++ htmlxref.1.cnf
@@ -478,5 +478,5 @@
  scantest      node    ${METAEXCHANGE}/scantest.html

-MIT_SCHEME = ${GS}/mit-scheme/documentation
+MIT_SCHEME = ${GS}/mit-scheme/documentation/stable
  mit-scheme-ref          node  ${MIT_SCHEME}/mit-scheme-ref/
  mit-scheme-user  node ${MIT_SCHEME}/mit-scheme-user/


All the best,
Thérèse