Update paged_scope to use AREL.

AssociationCollection#scoped() does not accept args in rails 3.
Fix include for pagem.rb.
Update for rails 3.1.
Drop rails 2 app, used by test suite.
Add 3.1 app for test suite.
Update #paged_scope spec for 3.1 changes.
Drop some unused requires.
Update for 3.1 changes.
rake manifest.
rake release
s/mock/double/
Update #paged_scope() to return an empty scope instead of an array.

So we can check #exists?() in app code.
Merge pull request #1 from mdsol/feature/rails3

Feature/rails3