patch 9.0.0206: redraw flags are not named specifically

Problem:    Redraw flags are not named specifically.
Solution:   Prefix "UPD_" to the flags, for UPDate_screen().
diff --git a/src/message.c b/src/message.c
index ec43387..715c7be 100644
--- a/src/message.c
+++ b/src/message.c
@@ -1138,7 +1138,7 @@
     FILE	*save_scriptout;
 
     if (redraw == TRUE)
-	must_redraw = CLEAR;
+	must_redraw = UPD_CLEAR;
 
     // If using ":silent cmd", don't wait for a return.  Also don't set
     // need_wait_return to do it later.
@@ -1362,7 +1362,7 @@
 	    && (redraw == TRUE || (msg_scrolled != 0 && redraw != -1)))
     {
 	starttermcap();		    // start termcap before redrawing
-	redraw_later(VALID);
+	redraw_later(UPD_VALID);
     }
 }
 
@@ -2485,8 +2485,8 @@
     }
 #endif
     ++msg_scrolled;
-    if (must_redraw < VALID)
-	must_redraw = VALID;
+    if (must_redraw < UPD_VALID)
+	must_redraw = UPD_VALID;
 }
 
 /*