Merge pull request #8 from pimlott/master

More tests, a little doc.
use non-identity-affecting attributes in exact matches

Previously, implementations of getExactMatchStatement were filtering them
out (in contrast to implementations of getFuzzyLookupQuery).  This is
probably because findTuForSave doesn't want to search on them.  But
findTuForSave should take care of that itself.

Test included.