mesa: implement GL_ARB_texture_buffer_range

mesa: implement GL_ARB_texture_buffer_range

v2: Record texObj.BufferSize as -1 in TexBuffer(non-Range) instead
of the buffer's current size so we know we always have to use the
full size of the buffer object (i.e. even if it changes without the
user calling TexBuffer again) for the texture.

Clarify invalid offset alignment error message.

v3: Use extra GL_CORE-only section in get_hash_params.py for
TEXTURE_BUFFER_OFFSET_ALIGNMENT.

v4: Remove unnecessary check for profile in _mesa_TexBufferRange.
Add check for extension enable in get_tex_level_parameter_buffer.

v5: Fix position in gl_API.xml.
Add comment about meaning of BufferSize == -1.

v6: Add back checks for core profile and add a note about it.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>