[Paraview] paraview.5.1.renderingbackend.opengl on server and paraview.5.1.renderingbackend.opengl2 on client

[GUILBAUD Claire]

Hi John,

It is written in the code that you can't have a client in OpenGL and a 
server in OpenGL2 on the server. But you can have a pvserver with mesa 
with backend opengl2.
When you build ParaView with Mesa, you have to choose a backend. This 
means that you must build 2 times ParaView for Mesa, one for each backend.
When running paraview (client), you have to choose the good pvserver 
(same backend than the client). Thus the hand shake strings should be 
the same.

Claire