In pci_6600.c (as well as other files corresponding to various machine types)
there is a setting for PCI_STRAY_MAX, which is set to 5.  I've bumped this
number up and I've currently got 33 'stray interrupt' messages logged..
however, I'm not seeing the hang problem I had after the previous max
of 5 when it would stop logging.  This seems like an okay work around for
now, but I'm unsure of the real implications of stray interrupts..