BUG #14828: Keep surface color from interacting with scalar color.

When using scalar coloring, if vtkScalarsToColorsPainter decided to use
a texture for mapping the scalars to colors, we ended up with the
surface color bleeding through the texture. This commit ensures that
such bleeding is avoided.

We don't simply use glTexEnvf (GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE,
GL_REPLACE), since that results in the diffuse highlights being lost.
By enabling GL_COLOR_MATERIAL and calling glColor3f(1,1,1), we follow
the same lighting/coloring path as we would when not using the texture
for scalar coloring.

Change-Id: I9c4db15dd0db699d5d045fa7ae27696d18828988
Merge topic '14828_scalar_coloring' into master

daf8c6e7 BUG #14828: Keep surface color from interacting with scalar color.