Transpose region STARTR1 to ENDR1 with STARTR2 to ENDR2.
The regions should not be overlapping, because the size of the buffer is
never changed in a transposition.
Optional fifth arg LEAVE-MARKERS, if non-nil, means don't update
any markers that happen to be located in the regions.
Transposing beyond buffer boundaries is an error.
(fn STARTR1 ENDR1 STARTR2 ENDR2 &optional LEAVE-MARKERS)