patch 8.0.1609: shell commands in the GUI use a dumb terminal

Problem:    Shell commands in the GUI use a dumb terminal.
Solution:   Add the "!" flag to 'guioptions' to execute system commands in a
            special terminal window.  Only for Unix now.

src/version.c

@@ -766,6 +766,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1609,
 /**/
     1608,
 /**/