Take source artifact properties into account when change tracking.

When properties on source files change, rules might have to be re-
applied and the installation of the respective source file may
have to be re-done. The current code catches none of that.

Change-Id: I7d87eb1d6bbb9918f2633ec8cbb9640ca23b90a4
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>
Fix build data rescuing.

The old implementation allowed more than one connection
to a child with the same file path represented by
different artifact objects.

Change-Id: I38db86c50f0f671fdcb05d481f51fb512442cbfd
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>