TestLogoWidgetDepthPeeling, TestLogoWidgetAlphaBlending.
These two tests look like they were trying to disable multisampling
by calling SetMultiSamples(1), where VTK's default number of
multisamples is 8.  However, on at least one system (OS X 10.5 with
Radeon 9600 XT) these tests fail unless the sample buffer is disabled
completely.

Change-Id: I287933920cd78d02b34ab44a2d765deebd7d6b3a