Got the selection start and end handle dragging working... The trick was not
to call SwWrtShell::SetCursor(), but SwCrsrShell::SetCrsr(). Sounds easy but
took a lot of guessing and experimentation to figure out. Anyway, now it does
what I had expected it to do a few das ago already.

There are glitches, especially in corner cases like if you move the start
handle past the end handle or vice versa.

more

Change-Id: Id6c1d99a4052531789bccf0d48165cfb41b89cfe
9b94c0dd55b04a7b6b3c40654562a9c51fa9b450