Function: mouse-start-end

Return a list of region bounds based on START and END according to MODE.
If MODE is 0 then set point to (min START END), mark to (max START END).
If MODE is 1 then set point to start of word at (min START END),
mark to end of word at (max START END).
If MODE is 2 then do the same for lines.
(fn START END MODE)