This patch provides a way to optionally suppress spurious interrupts,
as a workaround for systems described below:

Some old operating systems do not handle spurious interrupts well,
and qemu tends to generate them significantly more often than
real hardware.

Examples:
  - Microport UNIX System V/386 v 2.1 (ca 1987)
    (The main problem I'm fixing: Without this patch, it panics
    sporadically when accessing the hard disk.)
  - AT&T UNIX System V/386 Release 4.0 Version 2.1a (ca 1991)
    See screenshot in "QEMU Official OS Support List":
    http://www.claunia.com/qemu/objectManager.php?sClass=application&iId=9
    (I don't have this system to test.)
  - A report about OS/2 boot lockup from 2004 by Hampa Hug:
    http://lists.nongnu.org/archive/html/qemu-devel/2004-09/msg00367.html
    (My patch was partially inspired by his.)
    Also: http://lists.nongnu.org/archive/html/qemu-devel/2005-06/msg00243.html
    (I don't have this system to test.)
Signed-off-by: NMatthew Ogilvie <mmogilvi_qemu@miniinfo.net>
Signed-off-by: Nmalc <av1474@comtv.ru>