add arc glyph
Squashed 'subtree/bokehjs/' changes from b873e98..4ef354b

4ef354b fix typo in default for direction property of arcs
b7f434d add back fast_path check in circle, turn on fast path for grid demo and make 2x2
c7a5c1c better results with 2x2 grid but still issues (toolbar positions)
78931da grid plot side by side works
49b77ab fix improper saving of ymapper state
aa1d0b2 remove spurious build_mappers code in tools causing unecessary extra computation of computed properties
9283822 remove spurious views adversely affecting performance
474c99b add TODO for gmap plot throttling
f151143 Merge branch 'master' of github.com:ContinuumIO/bokehjs
1b79db5 Fixing GridPlot and grid_plot example
496eae3 remove (accidentally checked in) .DS_Store files

git-subtree-dir: subtree/bokehjs
git-subtree-split: 4ef354b44986a6e7ebe2fbf15fd8d65294817485
Merge commit '5d867ffd5cb39743d0f6c4f4d1379faf58f063b2'
add bezier and quadratic glyphs