Fix test_finding_with_cross_table_order_and_limit for Oracle

[rsim]

Use latest Arel syntax and pass each order by expression as separate argument to order method as otherwise invalid Oracle SQL is generated.

[raviolicode]

@rsim, this test's syntax was made on purpose, for the fix on issue #1720, details on the commit are on this pull request.

Looking at the code, maybe this fix can be easily ported by updating here?

[rsim]

@raviolicode Sorry, didn't notice that it was on purpose :)
Because of this test my ActiveRecord on Oracle build was broken http://ci.rayapps.com/job/rails-master-activerecord-oracle/129/build_ruby=1.8.7/console

I would prefer to deprecate this old style of passing all order by as one string as in Oracle case I need to split it into array and splitting of this string is quite tricky (as commas can be used to separate function arguments as well). Or if it is still working in MySQL and PostgreSQL and SQLite3 then maybe make this test just for these databases.