complain about absent files to -pro argument (in lupdate)

sync up; this doesn't actually do anything in creator (or qmake).

Change-Id: I908fc3792bdc321370e51be98adf7a9c81e37a85
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>
(cherry picked from qtbase/15981b985fa3ae250af22f68ddb50e08bd9ce421)