Use validity extent to generate default resolutions

Previously, the TiledWMS source generated a resolutions array
derived from the world extent in meters, to match the default
Web Mercator resolutions of the map. This wouldn't work for
projections with distance units different than meters. It is
better to commit to a default resolutions array where zoom level
0 is the validity extent of the projection (not the Web Mercator
world extent!) at a 256 pixel tile size.
Use a loop rather than tileRange.forEachTileCoord
Move closure out of loop, and use loop rather than forEachTileCoord
Remove forEachTileCoord
Structure DOM renderer code to be more similar to WebGL renderer code
Remove unused requires
Join short lines
Move var outside loop
Add function to chose renderer from query string
Update examples to read renderer from query string
Merge pull request #115 from twpayne/renderer-clean-ups

Renderer clean ups
Fire postrender events
Merge pull request #117 from twpayne/postrender-event

Fire postrender events
Refactor mouse position control to use postrender event
Update mouse position on each frame
Merge pull request #118 from twpayne/mouse-position-control-refactoring

Mouse position control refactoring
Update Bing maps key
Merge pull request #91 from elemoine/bingkey

Bing maps key will expire on 15 Jan 2013
Add ol.Rectangle.extend
Merge pull request #114 from ahocevar/resolutions

Use validity extent to generate default resolutions. r=@twpayne,@elemoine