Fix bad SetColor/GetColor interaction in vtkProperty.

The SetColor() method calls SetAmbientColor(), SetDiffuseColor(),
and SetSpecularColor() and each of these can potentially trigger
a ModifiedEvent.  However, if the ModifiedEvent callback calls
GetColor(), which it often will, this causes Bad Things to happen
because GetColor() calls ComputeCompositeColor() which re-computes
this->Color based on the values of AmbientColor, DiffuseColor, and
SpecularColor.  The fix is to make sure that Modified() is not
called until all of the ivars have been set.

Change-Id: I00a6799a1a9e31a6b28e102e11e4a6bd71f18d71
Merge topic 'property-setcolor' into master

170d6649 Fix bad SetColor/GetColor interaction in vtkProperty.