[Piglit] ARB_copy_buffer

[Eric Anholt]

New Tokens

    Accepted by the target parameters of BufferSubData,
    GetBufferSubData, GetBufferPointerv, MapBufferRange,
    FlushMappedBufferRange, GetBufferParameteriv, BindBufferRange,
    BindBufferBase:

    COPY_READ_BUFFER                    0x8F36
    COPY_WRITE_BUFFER                   0x8F37

Other things I can think to test that aren't tested:

- large copy sizes, to hit i965's > (1 << 16) cases.
- larger copy sizes, to test aperture size limits.
- synchronization with vertex reads.
- synchronization with PBO reads/writes.
- synchronization with TF.
- synchronization with ARB_mbr.
- synchronization with itself.