Make maximum number of tiles loading a parameter to loadMoreTiles
Boost number of loading tiles when not animating or interacting
Only reprioritize tile queue when more tiles will be loaded
Compute number of new tiles to load exactly
Assert that loadMoreTiles is only called when more tiles will be loaded
Only manage the tile queue if it is not empty and improve comment
Merge pull request #498 from twpayne/boost-tile-loading

Boost tile loading