[Piglit] depthstencil-render-miplevels for GL_TEXTURE_2D_ARRAY

[Chad Versace]

If you care about 2d-array depthbuffers, I've extended depthstencil-render-miplevels
to handle that case. You can find it here:

   git://people.freedesktop.org/~chadversary/piglit.git branch=depthstencil-cruelty

The branch isn't ready for publication yet. I wanted to inform people, though, in
case anyone was working on related driver code. As expected, many 2d-array tests
fail on Ivybridge.

You can run it in 2d-array mode like this:
   depthstencil-render-miplevels GL_TEXTURE_2D_ARRAY width0 height0 num_layers buffer_combination