Added documentation about interaction between `subqueryload` and LIMIT/OFFSET.
Small improvement on FlushError can't delete error message

Output in the error message the table name and the column name.
Merge pull request #148 from pbu88/small_error_reporting_improvement

Small improvement on FlushError can't delete error message
Merge branch 'subqueryload_order' of https://bitbucket.org/univerio/sqlalchemy into pr26
- edits to the subqueryload ordering merge