Interlisp
Fixes recently identified glitches, eliminates some code duplication, removes inessential STREAMHINT back references
This replaces PR #1673, which should be closed and deleted when this is merged.
BOUT (printing) should work better (but see issues in #1701), Move should be properly undoable (and undo-undoable), offscreen scrolling on the left should not garble the display.
The STREAMHINT xpointer field is still present but now only for its essential uses in line formatting and display. Those still need to be examined.
Remnants of an old strategy for screen updating were removed, hopefully will make it easier to fix lingering bugs.
Note that typing at the bottom of the screen still scrolls to the top rather than going up just a big to reveal the new caret line--next time.
With respect to undoing Move, undoing where the source and target are in the same document puts that document back to its previous state. But if the source was taken from, and deleted in, a different Tedit document, undo doesn't undo the source deletion. If that document had been changed after the move, the deleted material would be inserted at some arbitrary place. (It would be easy to detect whether the source document is in its original state so that the deletion could be sensibly undone. But that would require back-pointers between separate documents, causing either a circularity (using pointers) or the possibility of smashing a previously collected and perhaps reallocated structure (with xpointers).)
