[TACHYON-220] WIP Comments describing issues and possible solutions 

Some initial comments to help improve the performance of master info. From what I gather there is locking on stack local objects that are never really put back into the map. I would appreciate suggestions before implementing it, hence the WIP tag.
Yeah, pretty much all the MasterInfo methods have a helper method that starts with an underscore, like _addCheckpoint, _createFile, _delete, _ls, etc.