Merge the multihead-1-0-0 branch into the trunk, with the exception of the

    glide header files.
The changes include:
- Brian Paul's changes to the tdfx client-side 3D driver to make it
    dlopen() the correct glide library (Voodoo3 or Voodoo5). This allows
    both types of the glide library to co-exist, and allows Voodoo3/Voodoo5
    cards to be mixed in multi-head configs.
- DRM kernel driver changes to allow a driver to set up multiple instances
    (minor numbers), one for each card present that the driver supports.
    This is currently implemented and tested only for the tdfx DRM driver.
- Add some missing missing <stdarg.h> includes.
- Some log message cleanups.
- Change the 2D tdfx driver to access VGA legacy registers via their PCI
    I/O space access points rather than their legacy addresses, and fix
    some problems with the way the VGA-related bits are initialised.
Status:
- With these changes, multi-head direct rendering works with multiple
    Voodoo3 and/or Voodoo5 cards. This has been tested with two PCI Voodoo3
    cards and an AGP Voodoo5 card, and all permutations of those.
Caveats:
- Xinerama is not supported. If Xinerama is enabled, then direct rendering
    gets disabled.
- The text mode on secondary screens will show junk after the X server
    exits.
- On some hardware, starting the X server on multiple 3dfx cards will
    result in a hard lockup. One workaround is to enable APIC support in a
    uni-processor kernel, or use an SMP kernel.