Copyright (c) 2012 Kevin Wellwood
All rights reserved.
This source code is distributed under the Modified BSD License. For terms and
conditions, see license.txt.
Returns a Resource_File in the cache, or loads it if it hasn't been
loaded. If 'needLock' is True, the cache's lock will be taken and
released. null will be returned on error.
Preloads a file from disk if it hasn't been loaded, starting the
reference count at 0. If 'needLock' is True, the cache's lock will be
taken and released.
Releases a reference to a Resource_File in the cache. If all
references to the resource have been released, the resource made be
removed from the cache. If 'needLock' is True, the cache's lock will
be taken and released.