Fixed selecting DISTINCT rows from a table when ordering by a column that is not
part of the SELECT list where the join creates at least one extra row.

While previously the test suite combined with Rails 4.0.0 looked like it worked, the
constructed SQL would return incorrect values for
FinderTest#test_find_with_order_on_included_associations_with_construct_finder_sql_for_association_limiting_and_is_distinct.
By using a GROUP BY and MAX()/MIN() in the ORDER BY with no DISTINCT call, the order
of the returned rows was not necessarily correct.

With Rails 4.0.1, a related bug was fixed that introduces a new method,
columns_for_distinct. Unfortunately by adding the columns from the ORDER BY clause
to the SELECT list, the DISTINCT nature of the queries was altered. This combined
with a test limiting the results to only 2 records, exposed the bug.

From testing various SQL constructs to solve the issue, I ended up determining that
to properly return a single value from the related table used in the ORDER BY, a
query with a subquery utilizing ROW_NUMBER() and DENSE_RANK() was needed. The
ROW_NUMBER() was partitioned over the originally requested columns, and then the
outer query would filter the results to just the first row of each partition.
DENSE_RANK() was used to generate a proper ordering of the partitions in relation
to each other.

In the process I also determined that extra code, plus an extra test, was necessary
to ensure that when such a construct was generated using both a limit and offset,
that the results would be correct also.

See https://github.com/rails-sqlserver/activerecord-sqlserver-adapter/issues/306
for further discussion, plus example queries and results.
Merge pull request #329 from veracross/fix-distinct-plus-limit

Fix for Issue #306 - DISTINCT + TOP + ORDER BY Associated Table