[FIX] #793 Partial Sharing overwrite non shared files 

Do not transmit files that are modified but not shared
in a partial shared session.

Change-Id: I4b78f05c7f31aa24d925774a31d5279afd57435e
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/681
Tested-by: Jenkins CI
Reviewed-by: Franz Zieris <zieris@inf.fu-berlin.de>
Reviewed-by: Arndt Lasarzik <alasarzik@gmail.com>
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>