Make fixes for VTK 6, QT 5 and VS2012

The VTK 6 fixes are based on pull #218: https://github.com/PointCloudLibrary/pcl/pull/218.

The QT 5 fixes are from https://bitbucket.org/manctl/pcl/commits/095d858dd4f843ecfa637708d25a5202467f44d1, with a work around for QT bug 29331: https://bugreports.qt-project.org/browse/QTBUG-29331.

There are also two fixes on missing PCL_EXPORTS.

This version doesn't change any algorithm.