BGE: fix [#32775] LibFree crashing

Used the engine's RemoveScene (which ultimately calls the converter's RemoveScene) instead of the converter's RemoveScene when the converter free a blend file. This handles the scene removal in a safer fashion and solves the crash described in part 2 of the bug report. Part 1 no longer appears to cause a crash.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@57626 954f8c5b-7b00-dc11-b283-0030488c597c
Code cleanup: fix some vs2012 compiler warnings

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@57633 954f8c5b-7b00-dc11-b283-0030488c597c
Fix #35804: NVidia OpenCL render issue after sampler changes, workaround what looks like a compiler bug.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@57634 954f8c5b-7b00-dc11-b283-0030488c597c
Cycles OpenCL: make displacement and world importance sampling work.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@57636 954f8c5b-7b00-dc11-b283-0030488c597c
Fix #35812: cycles image texture node not doing proper alpha handling of PNG
images with open shading language enabled.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@57637 954f8c5b-7b00-dc11-b283-0030488c597c