Fix segfault if client queries for non-existent file by name.

If the client, usually Nautilus, ends up trying to find a file
by name instead of ID, there might not be a match. We should
return NOT_FOUND explicitly, as there is no libmtp error generated
in this case.

This situation arises after:
* A file is renamed
* A directory is created
* A file is created (which actually fails)

Refreshing the Nautilus view will get Nautilus back in sync.
Fix hopelessly short timeout in file transfers.

The client code was using the default 25 second timeout for
file transfer operations, which is far too short.
Add display name support to gvfs-ls.
Ubuntu: Shared libgvfscommon