Speed up loading of game.

Instead of "downloading" the game from the local filesystem, the
"httpfs" filesystem is used to allow the NaCl module to load the game
without download from an extrenal URL.
Bump to version 6.

Bump to the next version. I will upload to the Chrome WebStore after
this so that the new changes will be used. Changes in this release have
to do with disabling the "downloading" screen and speeding up the
loading process.