MFreeStencil [FirstBitmap.w[,LastBitmap.w]] ; Free's a Bitmap's stencil, a range of stencils or all stencils

Free's a specific, all or a range of previously-created stencils in
previously-created chunky Bitmap objects. Only the stencil is freed. If the
parameters are omitted all stencils in any created chunky Bitmaps will be freed.
If you specify the second parameter then a range of bitmap's stencils will be
freed.