locking in zipfs demo

[Alan Bateman]

Joel Uckelman wrote:
> I'm puzzled by the ReentrantReadWriteLock used in ZipFilePath in various
> place. It seems to be locking calls to getResolvedPathForZip(), which
> sets the pathToZip member if it's null. Is there a reason for using a
> lock for this instead of making pathToZip volatile like the offsets
> ArrayList is?
>   
It looks like it was intended to support asynchronous close of the zip 
file system, in which case it should be using fs.begin() and fs.end() 
rather than its own lock (Rajendra - can you confirm this?).

-Alan.