1) I modified the cab config site file to use gcc 4.9.2 and switch back
   to mesa. I also updated Nektar++ to 4.4 and Pyside2 to the 8-30 version.
   I also updated the script that runs the regression suite to work
   with gcc 4.9.2.

2) I updated build_visit to be able to correct an error building mesa with 
   gcc 4.8.2 or 4.9.2.



git-svn-id: http://visit.ilight.com/svn/visit/trunk/src@31546 18c085ea-50e0-402c-830e-de6fd14e8384