Includes the addition of an onSetCursor() handler which must be called
from both the GAL canvas AND the GAL backend (at least on OSX) to prevent
cursor flickering between (for instance) pencil and arrow.
Also includes new architecture for point editors which allows them to
coordiate cursors with the editing tools (so we can switch to an arrow
when over a point).
Wayne Stambaugh
Seth Hillbrand
Jeff Young