Call input.open() not open()

This cursor is already open, and doesn't get closed. I don't know
why it was calling open()
Rebind the input with the new hkey before opening
merge ScottDugas: reopen the same cursor that was closed.

Merge pull request #1598 from ScottDugas/sql-layer/mt-cursor-exception
https://github.com/FoundationDB/sql-layer/pull/1598