unset XMODIFIERS by default, in order to prevent total loss of key events seen on Fedora 18/19;

--- a/Admin/Linux/Isabelle	Wed Oct 02 19:27:12 2013 +0200
+++ b/Admin/Linux/Isabelle	Wed Oct 02 19:43:58 2013 +0200
@@ -19,6 +19,9 @@
 
 # main
 
+#paranoia setting -- avoid problems of Java/Swing versus XIM/IBus etc.
+unset XMODIFIERS
+
 exec "$ISABELLE_HOME/contrib/jdk/${ISABELLE_PLATFORM64:-$ISABELLE_PLATFORM32}/bin/java" \
   "-Disabelle.home=$ISABELLE_HOME" \
   {JAVA_ARGS} \

--- a/etc/settings	Wed Oct 02 19:27:12 2013 +0200
+++ b/etc/settings	Wed Oct 02 19:43:58 2013 +0200
@@ -22,6 +22,9 @@
 classpath "$ISABELLE_HOME/lib/classes/scala-compiler.jar"
 classpath "$ISABELLE_HOME/lib/classes/scala-reflect.jar"
 
+#paranoia setting -- avoid problems of Java/Swing versus XIM/IBus etc.
+unset XMODIFIERS
+
 
 ###
 ### Interactive sessions (cf. isabelle tty)

--- a/src/Doc/JEdit/JEdit.thy	Wed Oct 02 19:27:12 2013 +0200
+++ b/src/Doc/JEdit/JEdit.thy	Wed Oct 02 19:43:58 2013 +0200
@@ -244,6 +244,13 @@
 
   \textbf{Workaround:} Disable such effects.
 
+  \item \textbf{Problem:} Linux: some X11 input methods such as IBus tend
+  to disrupt key event handling of Java/Swing.
+
+  \textbf{Workaround:} Do not use input methods, reset the environment
+  variable @{verbatim XMODIFIERS} within Isabelle settings (default in
+  Isabelle2013-1).
+
   \item \textbf{Problem:} Linux: some X11 window managers that are not
   ``re-parenting'' cause problems with additional windows opened by the Java
   VM. This affects either historic or neo-minimalistic window managers like