Using QFileDialog directly on OS X can hang intermittently due to Qt
bug.

I was unsure how to update the QwtPlotPrintFilter code, so I just commented it out with a FIXME.

qgcunittest.pro now compiles and runs as long as run in terminal in projcts->Run Settings is unchecked.

Added a check for a division by zero in AbstractCalibrator::logAverage(). This was causing a crash when attempting a calibration when there's no RC data being received.