back to old-fashioned GC, which appears to work better with interactive applications;

--- a/etc/settings	Mon Aug 31 18:59:27 2015 +0200
+++ b/etc/settings	Wed Oct 07 13:53:44 2015 +0200
@@ -14,7 +14,7 @@
 
 ISABELLE_SCALA_BUILD_OPTIONS="-encoding UTF-8 -nowarn -target:jvm-1.7 -Xmax-classfile-name 130"
 
-ISABELLE_JAVA_SYSTEM_OPTIONS="-server -XX:+UseG1GC -XX:+UseStringDeduplication -Dfile.encoding=UTF-8 -Disabelle.threads=0"
+ISABELLE_JAVA_SYSTEM_OPTIONS="-server -Dfile.encoding=UTF-8 -Disabelle.threads=0"
 
 classpath "$ISABELLE_HOME/lib/classes/Pure.jar"