NAME
        AllocRaster -- allocate space for a bitplane.

   SYNOPSIS
        planeptr = AllocRaster( width, height )
           d0                    d0     d1

        planeptr allocraster(ulong,ulong);

   FUNCTION
        This function calls the memory allocation routines
        to allocate memory space for a bitplane "width" bits
        wide and "height" bits high.

   INPUTS
        width   - number of columns in bitplane
        height  - number of rows in bitplane

   RESULT
        planeptr - pointer to first word in bitplane, or NULL if
                   it was not possible to allocate the desired
                   amount of memory.

   NOTES
        In order to assure proper alignment of display memory, the
        allocbitmap() function should be used instead of allocraster
        when you wish to allocate display memory (rasters which are
        attached to a viewport or screen).

   BUGS

   SEE ALSO
        freeraster() graphics/gfx.h