softpipe: Take all lods into account when texture sampling.

softpipe: Take all lods into account when texture sampling.

This patch churns a lot because it needs to change 4-wide filters into
single pixel filters, since each fragment may use a different filter.

The only case not entirely supported is the anisotropic filtering.
Not sure what we want to do there, since a full quad is required by
that filter.

Signed-off-by: Olivier Galibert <galibert@pobox.com>
Reviewed-by: Brian Paul <brianp@vmware.com>