Add missing dependencies on goog.array
Use in-place filtering for post-render functions
Use for loop for iterating over layers
Use in-place filtering for pre-render functions
Remove dependency on goog.array
Merge pull request #140 from twpayne/array-clean-ups

Array clean ups
Replace ol.overlay.Overlay with ol.AnchoredElement

This commit adds several features:
- rename of class to better reflect its behaviour
- full ol.Object support
- integration with postrender event for integration with animations and
  render loop
- minimised DOM modifications
- more precise positioning
- element placed in DIV to avoid modifications to user-supplied element
- correctly handle changes to the positioning property