NAME
        CreateBehindLayer -- Create a new layer behind all existing layers.

    SYNOPSIS
        result = CreateBehindLayer(li,bm,x0,y0,x1,y1,flags [,bm2])
        d0                         a0 a1 d0 d1 d2 d3   d4  [ a2 ]

        struct layer *createbehindlayer(struct layer_info *, struct bitmap *,
            long, long, long, long, long, ... );

    FUNCTION
        Create a new layer of position and size (x0,y0)->(x1,y1)
        Make this layer of type found in flags.
        If SuperBitMap, use bm2 as pointer to real SuperBitMap,
        and copy contents of Superbitmap into display layer.
        If this layer is a backdrop layer then place it behind all
        other layers including other backdrop layers. If this is
        not a backdrop layer then place it behind all nonbackdrop
        layers.

        Note: when using SUPERBITMAP, you should also set LAYERSMART flag.

    INPUTS
        li - pointer to LayerInfo structure
        bm - pointer to common bitmap used by all layers
        x0,y0 - upper left hand corner of layer
        x1,y1 - lower right hand corner of layer
        flags - various types of layers supported as bit sets.
                (for bit definitions, see graphics/layers.h )
        bm2 - pointer to optional Super bitmap

    RESULTS
        result - pointer to layer structure if successful
                 NULL if not successful

    BUGS

    SEE ALSO
        deletelayer(), graphics/layers.h, graphics/clip.h, graphics/gfx.h