Arel/ActiveRecord compatibility

I found a couple of incompatibilities between Arel and ActiveRecord
where ActiveRecord handles a database structure but Arel doesn't so
that calling MyModel.first works fine, but MyModel.find does not.

The first problem is with non-standard SQL column types like PostGIS
geometry columns on a table.

The second problem is with mapping ActiveRecord classes to database
views instead of tables:

Good finds, Brian. We'll get these fixed up for 3.0 final.