hotfix for residual issues with FS#270; the artifacts still observed with radiosity abort-continue will now only show in the preview, but not in the generated image file.

corresponds to Perforce change 6086.
VS2010 kept reporting GUI project to be out of date even if it wasn't; fixed.

corresponds to Perforce change 6088.
preliminary workaround for FS#313 (radiosity.cpp pov::RadiosityFunction::BeforeTile assertion failed)

corresponds to Perforce change 6092.
various changes related to color computations.

corresponds to Perforce changes 6089, 6090, 6095, 6096, 6097, 6113.