fix path attribute
this was originally the path of the project, but from projectpath in the
backing data. the trouble with this is that projectpath now means nothing
as it is the legacy path before invent.
this is problematic because now you can /identifier/foo your way to a blob
but that blob won't tell you what the actual project path for that blob
is. to deal with this path is now the actual path on disk while
the legacy path is exposed as __do_not_use-legacy-projectpath until we
are sure nobody needs it anymore (which is likely dependent on having
a new well-defined life cycle states to represent when something is
in kdereview etc).