Remove terminated connections from the pool.

In pymssql, if you terminate a long running query manually
it will give you a connection reset by peer message, but this
connection remains in the pool and will be re-used.
Merge pull request #51 from sontek/pymssql_handle_terminated_connection

Remove terminated connections from the pool.
changelog, will merge to 0.8
Merge branch 'master' into rel_0_9