Upgraded the cx16 library to the Commander X16 Kernal ROM's prerelease 39.

libsrc/cx16/waitvsync.s

@@ -1,5 +1,5 @@
 ;
-; 2020-01-08, Greg King
+; 2021-04-01, Greg King
 ;
 ; void waitvsync (void);
 ; /* Wait for the start of the next video field. */
@@ -12,10 +12,10 @@
         .include        "cx16.inc"
 
 _waitvsync:
-        ldx     VIA1::PRA       ; (TIMER is in RAM bank 0)
-        stz     VIA1::PRA
+        ldx     RAM_BANK        ; (TIMER is in RAM bank 0)
+        stz     RAM_BANK
         lda     TIMER + 2
 :       cmp     TIMER + 2
         beq     :-              ; Wait for next jiffy
-        stx     VIA1::PRA
+        stx     RAM_BANK
         rts