Sql.rsql: Fix reconnect code.

The state-machine on the client side when the rsqld server
died was broken in several ways. It now seems to work.
Sql.rsql: Implement ping() API.

ping() now signals if any part of the connection was reconnected (1),
or has been broken (-1).
Sql.rsql: Default to not reconnect on broken connection.

This behaviour is in line with the other SQL modules,
and is necessary to avoid corruption due to lost state.
Sql.rsql: Implement {get,set}_charset().
Sql.rsql: Implemented support for all big_query() variants.

This implements support for big_typed_query(), streaming_query()
and streaming_typed_query().
Sql.rsql: Implemented generic proxy of functions.