Qnx: Fix broken qmake environment

Fix the way we parse PATH and LD_LIBRARY_PATH.

Change-Id: I9928bf3573728580af6f361ce30101d8db142fc2
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
QbsProjectManager: Clean up qbs::Preferences object.

Change-Id: I5921b97b42a94aaa9c06d47f8581538c12c4fcab
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>