None volor values properly propagate as null
Squashed 'subtree/bokehjs/' changes from b1c257d..c9a10b3

c9a10b3 better metrics for axis element extents
af2c620 nice angled date ticks for candle demo
3c2a0c5 improvement for datetime tick formatting

git-subtree-dir: subtree/bokehjs
git-subtree-split: c9a10b3420baf48ee116c733aa14567ad4625cb9
Merge commit '3ba9fbb4e9034c9a0d68c257a5f29fdcd0ad9978'
Merge branch 'master' of github.com:ContinuumIO/Bokeh
update built js