first issue:
vtk's opengl extension manager (base class for osmesa
extension manager) had changed in vtk 6.1. we were
overriding all the base class methods using a copy of
an out of date version of vtk class code. as a result
base class was not getting initialized and vtk's
open gl feature detection, driver, and gl identification
were not working.

To address this I got rid of the overrides that didn't
change vtk behavior and instead use the base class
implementation in those cases. this makes sure the
base class member variables get initialized and feature
detection etc works again.

second issue:
I also let visit enable the blend_function_separate
extension. in vtk this is the most efficient way
to ensure correct alpha values during transparent
rendering and is required for vtk's depth peeling
algorithm. In a number of plots in visit that need
a specific blend function I had to set the blend
function explicitly and save and restore the related
gl blending state.

note:
plots that make use of GL_SRC_ALPHA,GL_ONE_MINUS_SRC_ALPHA
mode for alpha blending don't produce correct alpha
values. I didn't change that here.


git-svn-id: http://visit.ilight.com/svn/visit/trunk/src@27366 18c085ea-50e0-402c-830e-de6fd14e8384