Satisfy JSLint

JSLint complains about functions being declared in blocks.
Merge pull request #225 from fredj/css-cleanup

Remove CSS color workarounds.
Make it explicit that functions operate on tile sources
Add ol.source.TileSource.useTile
Implement useTile for image tile sources with caches
Mark all low resolution tiles as used to prevent cache expiration
Merge pull request #224 from twpayne/jslint-clean-ups

Satisfy JSLint
Move useLowResolutionTiles from layer renderer to tile source
Avoid creating a TileCoord object when marking used tiles
Merge pull request #226 from twpayne/preserve-low-resolution-tiles

Preserve low resolution tiles
Add ol.DeviceOrientation