Added a check against open-apple during boot to route boot to slot 6

This happens after the first two blocks are loaded from the HD.

firmware/HDD/hddrvr.a65

@@ -54,6 +54,7 @@ diskblock = $46
 
 slot6   = $c600
 OS      = $0801
+BUTTON0 = $C061
 
 ; The Autoboot rom will call this.
 ; This is also the entry point for such things as IN#7 and PR#7
@@ -109,6 +110,7 @@ noerr0
  bcc hdboot
 
 ; no image ready, boot diskette image instead
+BootSlot6
  jmp slot6
 
 ;======================================
@@ -190,9 +192,11 @@ hdboot
  lda #$1
  sta command
  jsr cmdproc
- bcc goload
- jmp slot6
+ bcs BootSlot6 ;no jmp, -3 bytes
+ 
 goload
+ bit BUTTON0   ; button 0 pressed?, 4 cyc
+ bmi BootSlot6  ; 2 cyc not taken
 
 ; X=device
  ldx #$70	; Slot# << 4
@@ -286,7 +290,7 @@ SmartPort3
  bne cmdproc
 
 ;======================================
-; 15 unused bytes
+; 3 unused bytes
 
 ; $CsFE = status bits (BAP p7-14)
 ;  7 = medium is removable