uniform server startup like windows and macos, for improved robustness if jEdit is terminated abruptly;

--- a/Admin/Linux/Isabelle.run	Mon Aug 01 11:54:32 2016 +0200
+++ b/Admin/Linux/Isabelle.run	Mon Aug 01 13:51:17 2016 +0200
@@ -32,13 +32,8 @@
 #paranoia setting -- avoid problems of Java/Swing versus XIM/IBus etc.
 unset XMODIFIERS
 
-if "$ISABELLE_HOME/bin/isabelle" jedit_client -c
-then
-  "$ISABELLE_HOME/bin/isabelle" jedit_client "$@"
-else
-  exec "$ISABELLE_HOME/contrib/jdk/${ISABELLE_PLATFORM64:-$ISABELLE_PLATFORM32}/jre/bin/java" \
-    "-Disabelle.root=$ISABELLE_HOME" "${JAVA_OPTIONS[@]}" \
-    -classpath "{CLASSPATH}" \
-    "-splash:$ISABELLE_HOME/lib/logo/isabelle.gif" \
-    isabelle.Main "$@"
-fi
+exec "$ISABELLE_HOME/contrib/jdk/${ISABELLE_PLATFORM64:-$ISABELLE_PLATFORM32}/jre/bin/java" \
+  "-Disabelle.root=$ISABELLE_HOME" "${JAVA_OPTIONS[@]}" \
+  -classpath "{CLASSPATH}" \
+  "-splash:$ISABELLE_HOME/lib/logo/isabelle.gif" \
+  isabelle.Main "$@"