connection#insert no longer returns last inserted id

In rails 2.0, I have several postgres migrations that rely on @connection.insert returning the last inserted id. When I upgraded to the 2.1 gems, this stopped working, and #insert now returns nil. The docs still say that #insert should return the last inserted id.

Attached is a patch that adds a failing unit test for this behavior. Note: I couldn't find ANY tests for any of the DatabaseStatements methods. I created a new file, test/cases/database_statements_test.rb.