patch 8.0.0616: not always setting 'background' correctly after :hi Normal

Problem:    When setting the cterm background with ":hi Normal" the value of
            'background' may be set wrongly.
Solution:   Check that the color is less than 16.  Don't set 'background' when
            it was set explicitly. (Lemonboy, closes #1710)

src/version.c

@@ -764,6 +764,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    616,
 /**/
     615,
 /**/