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.
diff --git a/src/getchar.c b/src/getchar.c
index 1f7c7d1..ddb23dd 100644
--- a/src/getchar.c
+++ b/src/getchar.c
@@ -1244,7 +1244,7 @@
     int		todo = len;
 
     /* remember how many chars were last recorded */
-    if (Recording)
+    if (reg_recording != 0)
 	last_recorded_len += len;
 
     buf[1] = NUL;
@@ -1254,7 +1254,7 @@
 	c = *s++;
 	updatescript(c);
 
-	if (Recording)
+	if (reg_recording != 0)
 	{
 	    buf[0] = c;
 	    add_buff(&recordbuff, buf, 1L);
@@ -2007,7 +2007,7 @@
     init_typebuf();
     start_stuff();
     if (advance && typebuf.tb_maplen == 0)
-	Exec_reg = FALSE;
+	reg_executing = 0;
     do
     {
 /*