Allow JETTY_USER to run without `su`

https://github.com/eclipse/jetty.project/pull/35

Signed-off-by: btpka3 <btpka3@163.com>
diff --git a/jetty-distribution/src/main/resources/bin/jetty.sh b/jetty-distribution/src/main/resources/bin/jetty.sh
index 8cbb41c..043d205 100755
--- a/jetty-distribution/src/main/resources/bin/jetty.sh
+++ b/jetty-distribution/src/main/resources/bin/jetty.sh
@@ -445,7 +445,7 @@
         exit 1
       fi
 
-      if [ -n "$JETTY_USER" ] 
+      if [ -n "$JETTY_USER" ] && [ `whoami` != "$JETTY_USER" ]
       then
         unset SU_SHELL
         if [ "$JETTY_SHELL" ]