fbo: Only reuse depth/stencil attachments if the parameters match.

fbo: Only reuse depth/stencil attachments if the parameters match.

When the user attaches a texture to one of the depth/stencil
attachment points (GL_STENCIL_ATTACHMENT or GL_DEPTH_ATTACHMENT), we
check to see if the same texture is also attached to the other
attachment point, and if so, we re-use the existing texture
attachment.  This is necessary to ensure that if the user later
queries what is attached to GL_DEPTH_STENCIL_ATTACHMENT, they will not
receive an error.

If, however, the user attaches buffers to the two different attachment
points using different parameters (e.g. a different miplevel), then we
can't re-use the existing texture attachment, because it is pointing
to the wrong part of the texture.  This might occur as a transitory
condition if, for example, if the user attached miplevel zero of a
texture to GL_STENCIL_ATTACHMENT and GL_DEPTH_ATTACHMENT, rendered to
it, and then later attempted to attach miplevel one of the same
texture to GL_STENCIL_ATTACHMENT and GL_DEPTH_ATTACHMENT.

This patch causes Mesa to check that GL_STENCIL_ATTACHMENT and
GL_DEPTH_ATTACHMENT use the same attachment parameters before
attempting to share the texture attachment.

On i965 Gen6, fixes piglit tests
"texturing/depthstencil-render-miplevels 1024 depth_stencil_shared"
and "texturing/depthstencil-render-miplevels 1024
stencil_depth_shared".

Reviewed-by: Chad Versace <chad.versace@linux.intel.com>