Rename local functions and embed in anonymous namespace

The templated function vtkMapperScalarToTextureCoordinate was defined
within the implementation file for vtkScalarsToColorsPainter. An
identical function with the same name was also defined in the
implementation file for vtkMapper. As is done with multiply-defined
templated functions, the linker was selecting only one of these
definitions for use by both vtkScalarsToColors and vtkMapper,
which is obviously not desirable behavior, but which turned out
no to cause any problems because the definitions were the same.

Solved this problem by placing both function definitions in anonymous
namespaces. Also, reduce the size of the names of these functions to
exclude the class name prefix.

Change-Id: I7cd8533c383b9388846c2f72c0873c2201a9b395
Change clamping range for texture coordinates

When InterpolateScalarsBeforeMapping is on, vtkMapper and
vtkScalarsToColorsPainter would clamp texture coordinates to the range
[0, 1]. This lead to incorrect results if the range of the scalar
values associated with points that define a primitive were not
completely contained within the range of the color lookup table used
to color that primitive, e.g., a quad with scalar range [0,3] colored
by a color map with range [1,2], and the option
InterpolateScalarsBeforeMapping is on. In this case, the texture
coordinates should be in the range [-1, 2], not clamped to [0, 1].

Unfortunately, removing the clamping completely leads to another
problem. It turns out that some implementations of OpenGL do not
handle arbitrary texture coordinates of about 1000 or higher
correctly. To handle this, clamping has been retained, but to the
range [-1000, 1000]. Hopefully this covers most use cases.

Change-Id: I597c4c1b5f18af645fd6f54e90103321b20b8fb9
Turn on edge clamping

This will ensure that texture coordinates outside the range [0,1] will
map to either the first or last texel, depending on which side of the
range the texture coordinate falls, rather than a texture border color
of some blended combination of the border color and texel value.

Change-Id: I2a9731c48d264d9bed63f1db67b5ea4bca257224
Fixed errors exposed by changes to clamping of texture coordinates

Told the mapper to use the lookup table's range. Without doing that,
the mapper was using the range [0, 1] for the color map range instead
of approximately [-250, 250]. The somewhat correct (but wrong)
appearance of the original baselines was a side-effect of the
incorrect clamping. Baselines have been updated to reflect the
corrected color mapping.

Change-Id: I639c026cd6b889ab7416eb48695529423ffa0a82
Merge topic 'fix_colormap_texture_coords' into master

56b92366 Fixed errors exposed by changes to clamping of texture coordinates
95686b60 Turn on edge clamping
b807a6d6 Change clamping range for texture coordinates
8160c637 Rename local functions and embed in anonymous namespace