colour image texture to orient vectors.

DisplayOpts instance already has clip/modulate/colour images set.

vertex attribute divisors, as things get screwed otherwise.

so I'll keep this in.

for managing shader programs. GLVolume and GLLabel ported to use it,
everything else is broken.

Also fixed bug in glvolume_frag - clip value was not being inverted when
negative colour map in use.

hacky solution. Still don't know what's going on there, but it will work
until I get a diffusion image with a messed up qform/sform.

coloured by another image.

value of VectorOpts.clipImage, the glvolume or the glvector fragment
shader may be used. GLRGBVector updated to work with this new structure.
Other vector things are broken.

because I will otherwise have a naming collision in the vector stuff.

   being slightly mis-managed..
2. The first CanvasPanel has syncOverlayOrder set to true.

clippingRange properties.

another image - this will be needed by VectorOpts cmap, if I want to
re-use the GLVolume fragment shader.

modulate image. Gl14, GLLineVector not yet supported, and things in the
GLVolume class hierarchy are broken.

I'm doing wrong.

might be broken.

Nifti1 overlays. More of these changes to come, I'm sure.

class. Associated changes to RGB/Line/Vector code so they support
TensorImage overlays. More changes need to be made, methinks.

a general base class. Will be used by TensorImage.

regular attribute though. TensorImage can be created with data that was
not created/named a'la dtifit.