[Qt-interest] Suppressing non-Qt library warnings

[Nikos Chantziaras]

Using QImageLoader sometimes results in warnings from libpng, libmng, 
etc like these:

libpng warning: Ignoring gAMA chunk with gamma=0
libpng warning: Ignoring attempt to set negative chromaticity value
libpng warning: Ignoring attempt to set cHRM RGB triangle with zero area

or:

MNG error 1029: Chunk out of sequence; chunk TERM; subcode 0:0

It does not matter whether Qt uses its own, bundled version of the libs 
in question of the ones installed on the system.  Is there a way to 
suppress this stuff?