patch 8.1.0020: cannot tell whether a register is executing or recording

Problem:    Cannot tell whether a register is being used for executing or
            recording.
Solution:   Add reg_executing() and reg_recording(). (Hirohito Higashi,
            closes #2745)  Rename the global variables for consistency.  Store
            the register name in reg_executing.

src/version.c

@@ -761,6 +761,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    20,
 /**/
     19,
 /**/