The goals of the patch are as follows:
    1) Allow MAXSCREENS to be determined at run time instead of compile
       time (a new -maxscreens command line flag was added).
    2) Make minimal source-code changes to the tree:
       a) The name "MAXSCREENS" was not changed -- this allowed all of
          the loops that reference MAXSCREENS to remain unchanged.
       b) MAXSCREENSALLOC is a convenience macro that allocates and
          zeros memory, allowing 1-line changes to allocate code (and
          another line to check that allocation succeeded).  Memory is
          zero'd because many routines assume that the previous static
          allocations are zero'd.  The macro is also safe to call
          multiple times since there are places in the code where the
          first use of a MAXSCREENS-sized array is difficult to
          determine (or non-deterministic).
       c) In some cases, the existing code zeros the memory.  These
          calls are unchanged, but could be removed.
 
Some of the changes could not be tested because we do not have the
appropriate hardware available -- it would be possible to substitute
MAXSCREENSDEFAULT for MAXSCREENS in these code paths (i.e., and leave
them as compile-time configurable code paths):
    config/cf/iPAQH3600.cf
    config/cf/itsy.cf
    programs/Xserver/hw/darwin/quartz/fullscreen/fullscreen.c
    programs/Xserver/hw/kdrive/kxv.c
    programs/Xserver/hw/sun/sunInit.c
    programs/Xserver/hw/sunLynx/sunLyInit.c
    programs/Xserver/hw/xfree86/drivers/* [all the changes are similar]
    programs/Xserver/hw/xfree86/os-support/bsd/arm_video.c
    programs/Xserver/hw/xfree86/os-support/dgux/dgux_video.c
    programs/Xserver/hw/xwin/InitOutput.c