[PATCH 1 of 7] vfs: use propertycache for open

[Yuya Nishihara]

On Fri, 5 Aug 2016 15:26:48 +0100, Jun Wu wrote:
> I don't think this is correct, as the filesystem is mutable. Consider:
> 
>   vfs.open(path)
>   os.unlink(path)
>   vfs.open(path) # <= Wrong result using propertycache

It just caches "open" function. Basically it is open = __call__, but __call__
is provided by a sub class. I don't know which is the canonical form.