openedFile.

To make this work, add OpenCountMutex to inode.  This fixes a race
condition in considerDropInode().

conversion.

FileSystemConnector.

Test for this in ZipFs.

This fixes a potential race conditions in
FileSystemConnector.internalLookupWithNode, which did not take the
treeLock.

store.

Add test.

Finding the workspace for a given backing store is a common operation
that requires readdir, and should not be expensive.

Further simplifies code.

Deal with nonexistent mountpoints both in mount and umount

* simplifies code

* deal with GetPath() on deleted files

This may occur if we loose connection to the NFS server, for example.

branch do work.