The new code is based on timestamps, rather than delays. This eliminates the
need to update every timer in timer_process(), which cost a non-trivial amount
of CPU time on low-end machines.
This involved changes to every user of the timer code, so this change almost
certainly introduces bugs.
Misc ViRGE fixes.
Changes to memory mapping.
Changes to PCI handling.
Disabled 'AMI WinBIOS 486 PCI' due to incomplete chipset emulation.
Invalid GUS register reads no longer kill the emulator.