- extract I/O calls into a Protocol interface and implementations
- moved send_result_set_row to THD
- renamed end_statement to send_statement_status and moved to THD
- on THD renamed protocol to m_protocol and added getter/setter
- removed com_data from THD
- moved THD::client_capabilites to protocols and added
has_client_capability, remove_client_capability, add_client_capabilit
- changed method signature for dispatch_command
- moved send_result_metadata to THD and renamed it to
Protocol::send_result_set_metadata()  and split it into
send_result_metadata(), start_result_metadata(), send_field_metadata()
and end_result_metadata()
- renamed:
Protocol::prepare_for_resend() -> start_row()
Protocol::write()              -> end_row()
Protocol::remove_last_row()    -> abort_row()

(cherry picked from commit bc37dabbd3cb746f23d9c8c5458bfd699f7c3e44)

Conflicts:
	sql/CMakeLists.txt
	sql/protocol_classic.cc
	sql/query_result.cc
	sql/sql_parse.cc
	sql/sql_parse.h
	sql/sql_thd_api.cc