observe SCALA_HOME, if available;
no default classpath for scala-library.jar;

--- a/etc/settings	Thu Jul 02 22:18:02 2009 +0200
+++ b/etc/settings	Fri Jul 03 00:00:03 2009 +0200
@@ -66,14 +66,14 @@
 ### JVM components (Scala or Java)
 ###
 
+ISABELLE_JAVA="java"
 ISABELLE_SCALA="scala"
-ISABELLE_JAVA="java"
 
-if [ -e "$ISABELLE_HOME/contrib/scala" ]; then
-  classpath "$ISABELLE_HOME/contrib/scala/lib/scala-library.jar"
-elif [ -e "$ISABELLE_HOME/../scala" ]; then
-  classpath "$ISABELLE_HOME/../scala/lib/scala-library.jar"
-fi
+[ -z "$SCALA_HOME" ] && SCALA_HOME=$(choosefrom \
+  "$ISABELLE_HOME/contrib/scala"
+  "$ISABELLE_HOME/../scala"
+  "")
+[ -n "$SCALA_HOME" ] && ISABELLE_SCALA="$SCALA_HOME/bin/scala"
 
 classpath "$ISABELLE_HOME/lib/classes/Pure.jar"