NAME
        LockLayer -- lock layer to make changes to cliprects.

    SYNOPSIS
        LockLayer( dummy, l )
                   a0     a1

        void LockLayer( long, struct layer *);

    FUNCTION
        Make this layer unavailable for other tasks to use.
        If another task is already using this layer then wait for
        it to complete and then reserve the layer for your own use.
        (this function does the same thing as graphics.library/LockLayerRom)

        Note: if you wish to lock MORE THAN ONE layer at a time, you
            must call locklayerinfo() before locking those layers and
            then call unlocklayerinfo() when you have finished. this
            is to prevent system "deadlocks".

        Further Note: while you hold the lock on a layer, Intuition will block
            on operations such as windowsizing, dragging, menus, and depth
            arranging windows in this layer's screen.  It is recommended that
            YOU do not make Intuition function calls while the layer is locked.

    INPUTS
        dummy - unused
        l - pointer to a layer

    BUGS

    SEE ALSO
        unlocklayer(), locklayerinfo(), unlocklayerinfo(),
        graphics.library/locklayerrom(), graphics/layers.h, graphics/clip.h