Start abstract type for lfilter tests, and add corresponding classes for the types we want to test.
Start abstract type for lfilter tests, and add corresponding classes for the types we want to test.

git-svn-id: 003f22d385e25de9cff933a5ea4efd77cb5e7b28@5663 d6536bca-fef9-0310-8506-e4c0a848fbcf

lesserwhirls/scipy-cwt,jasonmccampbell/scipy-refactor,scipy/scipy-svn,jasonmccampbell/scipy-refactor,scipy/scipy-svn,jasonmccampbell/scipy-refactor,scipy/scipy-svn,lesserwhirls/scipy-cwt,jasonmccampbell/scipy-refactor,lesserwhirls/scipy-cwt,lesserwhirls/scipy-cwt,scipy/scipy-svn