exclude qbs subprojects from lupdate message collection

the qbs translations should come from the qbs lib itself.

requires qt 5.1.2 to have an effect.

Change-Id: I0aabeaf24d06c9070c2de6e5a0bb9a8ddd6c06c1
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>
avoid boolean argument trap: introduce QMakeParser::ParseFlag

Change-Id: I26ce032a1aa044e9a4da0c8708a4490b07374992
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>
(cherry picked from qtbase/0a1faaa9eb7807bf11d796c2eca624e2f3b378a7)