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/fileio.c b/src/fileio.c
index d34605c..428e408 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -9274,7 +9274,7 @@
 
     if (!did_cursorhold
 	    && has_cursorhold()
-	    && !Recording
+	    && reg_recording == 0
 	    && typebuf.tb_len == 0
 #ifdef FEAT_INS_EXPAND
 	    && !ins_compl_active()