QT_CLEAN_NAMESPACE constant is no more needed
This may theoretically affect applications created for Qt1 and Qt2,
but such applications require further modifications as well.
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Cherry picked and adapted from commit ff63338d in tqt3 from Slávek Banko <slavek.banko@axis.cz>
Signed-off-by: Michele Calgaro <michele.calgaro@yahoo.it>