( RLDICT pre-comment: Copy dict from target wordref, including
header, up to HERE.  We're going relocate those words by
specified offset. To do this, we're copying this whole memory
area in HERE and then iterate through that copied area and call
RLWORD on each word. That results in a dict that can be
concatenated to target's prev entry in a more compact way.

  This copy of data doesn't allocate anything, so H@ doesn't
move. Moreover, we reserve 4 bytes at H@ to write our target
and offset because otherwise, things get too complicated with
the PSP.

  The output of this word is 3 numbers: top copied address, top
copied CURRENT, and then the beginning of the copied dict at
the end to indicate that we're finished processing.
                                                        cont. )