patch 8.0.0507: client-server tests fail when $DISPLAY is not set

Problem:    Client-server tests fail when $DISPLAY is not set.
Solution:   Check for E240 before running the test.
diff --git a/src/version.c b/src/version.c
index e19da86..1f82ee1 100644
--- a/src/version.c
+++ b/src/version.c
@@ -765,6 +765,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    507,
+/**/
     506,
 /**/
     505,