patch 7.4.1992

Problem:    Values for true and false can be confusing.
Solution:   Update the documentation.  Add a test.  Make v:true evaluate to
            TRUE for a non-zero-arg.

src/version.c

@@ -758,6 +758,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1992,
 /**/
     1991,
 /**/