Squashed commit of the following (st-mesa-per-context-shaders branch):

Squashed commit of the following (st-mesa-per-context-shaders branch):

commit 4f106f44a32eaddb6cf3fea6ba5ee9787bff609a
Author: Brian Paul <brianp@vmware.com>
Date:   Mon Dec 13 14:06:08 2010 -0700

    st/mesa: reorganize vertex program translation code

    Now it looks like the fragment and geometry program code.
    Also remove the serial number fields from programs.  It was used to
    determine when new translations were needed.  Now the variant key is
    used for that.  And the st_program_string_notify() callback removes all
    variants when the program's code is changed.

commit e12d6791c5e4bff60bb2e6c04414b1b4d1325f3e
Author: Brian Paul <brianp@vmware.com>
Date:   Mon Dec 13 13:38:12 2010 -0700

    st/mesa: implement geometry shader varients

    Only needed in order to support per-context gallium shaders.

commit c5751c673644808ab069259a852f24c4c0e92b9d
Author: Brian Paul <brianp@vmware.com>
Date:   Sun Dec 12 15:28:57 2010 -0700

    st/mesa: restore glDraw/CopyPixels using new fragment program variants

    Clean up the logic for fragment programs for glDraw/CopyPixels.  We now
    generate fragment program variants for glDraw/CopyPixels as needed which
    do texture sampling, pixel scale/bias, pixelmap lookups, etc.

commit 7b0bb99bab6547f503a0176b5c0aef1482b02c97
Author: Brian Paul <brianp@vmware.com>
Date:   Fri Dec 10 17:03:23 2010 -0700

    st/mesa: checkpoint: implement fragment program variants

    The fragment programs variants are per-context, as the vertex programs.

    NOTE: glDrawPixels is totally broken at this point.

commit 2cc926183f957f8abac18d71276dd5bbd1f27be2
Author: Brian Paul <brianp@vmware.com>
Date:   Fri Dec 10 14:59:32 2010 -0700

    st/mesa: make vertex shader variants per-context

    Gallium shaders are per-context but OpenGL shaders aren't.  So we need
    to make a different variant for each context.

    During context tear-down we need to walk over all shaders/programs and
    free all variants for the context being destroyed.