Should be fixed on master by the commits below.  This bug shouldn't exist on 7.9 or 7.10 branches because the changes that caused it do not exist there.

commit e397b3a7c051b70a574e34096b70fc98e4e84b2c
Author: Ian Romanick <ian.d.romanick@intel.com>
Date:   Sat Apr 2 18:56:33 2011 -0700

    mesa: Add fall-back formats for unsupported snorm formats
    
    This is always the way with real hardware and desktop OpenGL.  Some
    hardware can't do some formats natively.  The alpha-only, luminance,
    and intensity formats are usually the most problematic.  Some sized
    formats can also be problematic.  This patch provides fall-back
    formats for those that are not natively supported.
    
    At some point it would be interesting to try providing
    device-independent conversions using EXT_texture_swizzle.  The drivers
    that support EXT_texture_swizzle could, for example, see
    GL_LUMINANCE16_SNORM as MESA_FORMAT_SIGNED_R16 with a { r, r, r, 1 }
    swizzle.  Care would need to be taken to prevent issues with using
    those textures for FBO rendering.
    
    This is the rest of the fix for glean's pixelFormats test on i965.
    
    Reviewed-by: Marek Olšák <maraeo@gmail.com>
    Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

commit ad3fbac00bb4430aa26f4dbd3a795715b0fc7fef
Author: Ian Romanick <ian.d.romanick@intel.com>
Date:   Sat Apr 2 18:49:13 2011 -0700

    i965: Add the missing supportable EXT_texture_snorm formats
    
    This class of hardware can natively sample all of the snorm surface
    formats that DX10 requires, but it can't do some of the legacy GL
    formats.  In particular, all of the alpha, luminance, and intensity
    formats are unsupported.
    
    This partially fixes the breakage in glean's pixelFormats test since
    GL_EXT_texture_snorm support was added to Mesa.
    
    Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

Verified with mesa master commit 0c501bacef3738b55986292abca149dcfe76d72d.