patch 7.4.757

Problem:    Cannot detect the background color of a terminal.
Solution:   Add T_RBG to request the background color if possible. (Lubomir
            Rintel)

src/version.c

@@ -741,6 +741,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    757,
 /**/
     756,
 /**/