Fix issue where newly inserted items end up in the wrong directory

Fix issue where newly inserted items end up in the wrong directory

If we have directory "a" and "a/b" and expand both, then collapse "a" we
tell KDirWatcher to stop watching both these directories.

However, KDirWatcher keeps them in the listersCurrentlyHolding list as
well as the listersCurrentlyListing list and will still notify of
changes. If a new file appears in "a/b/" we will still get change
notifications.

When dolphin processes these changes we cannot find the relevant parent
node. It then gets confused and inserts the item into the root directory
from the POV of the model notifications. When we then open the relevant
folder the model knows a node with that URL exists and fails to add it
correctly.

This can also be reproduced by continually downloading files into a
subdirectory tree and rapidly expanding and collapsing folders a few
levels deep.