Debugger: Add IRQ support to LBR and new command to Break on Interrupt (#987, PR #990)

Extend LBR so that it includes the control-flow on a taken interrupt
Add a new command 'brkint <0|1>' to support Break on Interrupt

Internal: in core emulation loop, moved IRQ/NMI check to start of loop so that just the "interrupt vectoring" case can be single-stepped (instead of previously opcode + interrupt vector).

Debugger help chm: update Breakpoints section to include BRK, BRKOP and BRKINT

source/Debugger/Debug.h

@@ -38,6 +38,7 @@
 		, BP_HIT_MEMR = (1 << 4)
 		, BP_HIT_MEMW = (1 << 5)
 		, BP_HIT_PC_READ_FLOATING_BUS_OR_IO_MEM = (1 << 6)
+		, BP_HIT_INTERRUPT = (1 << 7)
 	};
 
 	extern int          g_nBreakpoints;