[Coco] NitrOS-9 boot crash with clock2_smart and Disto SC-II no-halt driver

[Robert Gault]

K.Pruitt reported this problem and I confirmed that with Level2, the current 
clock2_smart and Disto SC-II no-halt driver can't coexist. I've found a fix for 
this but can't commit it to Sourceforge with the Mercurial system now in use.

If anyone else is having this type of clock and no-halt problem, here is the fix 
I came up with. You can compile a new clock_60hz or clock_50z module and see if 
it works with systems other than mine.

Current code in clock.asm  starting at line 192
; ldd	#$343C		[A]=PIA0 CRA contents, [B]=PIA0 CRB contents

   ifgt  Level-1
    ldd   #$3434     as per Robert Gault's suggestion
   else
    ldd   #$3435     IRQ needs to be left enabled for Level1, as no GIME 
generated IRQ
   endif

   sta   1,x        CA2 (MUX0) out low, port A, disable HBORD high-to-low IRQs
   stb   3,x        CB2 (MUX1) out low, port B, disable VBORD low-to-high IRQs

   ifgt  Level-1
    lda   ,x         clear possible pending PIA0 HBORD IRQ
   endc

You need to add a new line to disable the CART IRQ in the same fashion I 
disabled HSYNC and VSYNC for Level2.

   ifgt  Level-1
    sta   $23,x     !!!!!!!!!!!!!!!!!!!!!
    lda   ,x         clear possible pending PIA0 HBORD IRQ
   endc