Cpu simulator doesn't clear D flag on irq

[irmen]

It has come to light that the cpu simulation doesn't properly clear the Decimal (bcd) flag on IRQ and possibly other things. This is improved behavior of the 65C02 over the 6502 NMOS version, and the cpu simulator only seems to simulate the nmos variant's behavior here.

This causes issues: https://www.commanderx16.com/forum/index.php?/topic/3635-mouse_get-kernal-function-issue/

65c02 decimal flag behavior on irq, nmi, brk, reset: http://www.6502.org/tutorials/decimal_mode.html#5

At least the irq6502 routine should be improved: https://github.com/commanderx16/x16-emulator/blob/master/src/cpu/fake6502.c#L180 but most likely the nmi6502 as well and maybe others.