*
   NAME
        AttemptLockLayerRom -- Attempt to lock layer structure
                                         by ROM(gfx lib) code

   SYNOPSIS
        gotit = AttemptLockLayerRom( layer )
         d0                           a5

        bool attemplocklayerrom( struct layer * );

   FUNCTION
        Query the current state of the lock on this layer. if it is
        already locked then return FALSE, could not lock. If the
        layer was not locked then lock it and return true.
        This call does not destroy any registers.
        This call nests so that callers in this chain will not lock
        themselves out.

   INPUTS
        layer - pointer to layer structure

   RESULT
        gotit - TRUE or FALSE depending on whether the layer was
                successfully locked by the caller.

   SEE ALSO
        locklayerrom() unlocklayerrom()