Sandbox Broker now returns a handle to the exact path object that was
retained by the caller, so it will be released correctly, regardless of
what happens to the list of bookmarked paths.
Also refined the bookmark path comparison function. For existing paths,
it will find the first match. For new paths, it will prefer the longest
path instead, to try to find the deepest matching bookmark.
Signed-off-by: Christopher Snowhill <kode54@gmail.com>