Factor out core elements of ol.TileQueue into ol.structs.PriorityQueue
Refactor ol.TileQueue to extend ol.structs.PriorityQueue
Replace isHeap with assertValid
Add optional per-tile callback to manageTilePyramid
Store focus in frame state
Add tile texture queue
Use tile texture queue
Tune tile priority functions
Make tile pre-loading a per-layer option
Add preload example
Set preload appropriately in examples
Make preload a number of levels instead of a boolean
Correct preload example tags, thanks @fredj
Merge pull request #423 from twpayne/preemptive-webgl-texture-uploads

White flash occurs when zooming out from initially zoomed in view with WebGL renderer
Examples json and combined.js files in build dir
Remove unneeded test in build.py
Correct ns for ol.source.wms tests
Move Plovr json files in specific dir
Tests requireall.js generated in build dir
.gitignore clean-up