This is based on the notion that in Kicad the start and end-points
are far more important (as they usually connect to other segments)
than the center is.
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).
We were running into various corner conditions where a tool's event
loop would exit while the tool was still active, or the tool would
get popped while we were still in the event loop. (A lot of these
had to do with the POINT_EDITOR's, but not all of them.)
The new architecture:
1) tools always do a Push()/Pop()
2) everyone is responsible for their own pops; no more stack-clearing
on a cancel
3) CancelInteractive events go to all tools to facilitate (2)
If a tool called something like clearSelection while processing a
MOUSE_CLICK, the SELECTION_TOOL will pass the clearSelection
COMMAND_EVENT because it handles it as a transition, not as an
event. Because m_passEvent is effectively global, the tool manager
would then interpret that as passing the MOUSE_CLICK and we'd end
up processing the click by multiple tools.