Properly set the dirty rect to invalidate when points are added.
Don't draw points outside of the clip rect.
Merge branch 'dev' of https://github.com/garvankeeley/MozStumbler into point-draw-performance
basic hashing is working, need to hookup per-zoom
Recalc grid on zoom changed
Used ordered hash map, so that we can draw newest to oldest
Merge pull request #1040 from garvankeeley/point-draw-performance

1002: Point draw performance. Use hash of x and y to reduce number of points drawn