Divide ActiveRecord::ConnectionAdapters::OracleEnhancedColumnDumper
and ActiveRecord::ConnectionAdapters::OracleEnhancedSchemaDumper

To prepare merge rails4 branch into master,
these modules should be stored in separe file because
ActiveRecord::ConnectionAdapters::OracleEnhancedColumnDumper just supports
Rails 4 and does not Rails 3.2 and earlier versions.
Merge pull request #292 from yahonda/separate_column_dumper

Divide ActiveRecord::ConnectionAdapters::OracleEnhancedColumnDumper