more paranoia settings, e.g. relevant for Ubuntu 15.04;

--- a/etc/settings	Fri Apr 24 22:30:56 2015 +0200
+++ b/etc/settings	Fri Apr 24 23:05:33 2015 +0200
@@ -18,7 +18,11 @@
 
 classpath "$ISABELLE_HOME/lib/classes/Pure.jar"
 
-#paranoia setting -- avoid problems of Java/Swing versus XIM/IBus etc.
+#paranoia settings -- avoid intrusion of alien options
+unset "_JAVA_OPTIONS"
+unset "JAVA_TOOL_OPTIONS"
+
+#paranoia settings -- avoid problems of Java/Swing versus XIM/IBus etc.
 unset XMODIFIERS