Ght31

Bug fixes in the node cache.
The only loop over the entire node cache is in volatile.__enter__.  The other loops are over the list of watches or the list of volatile nodes, which should typically be very small, mostly 0 or 1.

The loop over the entire node cache in volatile.__enter__ could be a problem - it will happen every time a file is deleted or moved. The loop is only necessary if the node is a container node. I'll look at changing that.