X-Symbol mode -- look in canonical place;

--- a/etc/settings	Wed Aug 09 21:14:07 2000 +0200
+++ b/etc/settings	Thu Aug 10 00:45:23 2000 +0200
@@ -150,6 +150,11 @@
 fi
 PROOFGENERAL_OPTIONS=""
 
+# X-Symbol mode -- look in canonical place
+if [ -d "$ISABELLE_HOME/contrib/x-symbol" ]; then
+  XSYMBOL_HOME="$ISABELLE_HOME/contrib/x-symbol"
+fi
+
 
 ###
 ### External reasoning tools