Sort DisplayNode objects only when we have to.
Add the code that sorts a Layer._orderDrawBins object.
Remove a blank line.
Fix indents.
Merge branch 'develop' into hbono/sort-nodes
Merge branch 'develop' of https://github.com/tkihira/Tombo.js into hbono/sort-nodes
Merge branch 'develop' of https://github.com/tkihira/Tombo.js into hbono/sort-nodes
Fix styles.
Merge pull request #23 from tkihira/hbono/sort-nodes

Sort DisplayNode objects only when we have to