WITHOUT FILE AND SQL_THD NOT STARTED

Problem:
========
If, on an empty database:
- CHANGE MASTER TO without a MASTER_FILE and MASTER_POS is
  used
- the IO_THREAD is started WITHOUT starting the SQL_THREAD
- MySQL crashed
- MySQL is restarted with relay_log_recovery = 1.

Crash recovery will not work as expected:
- The IO_THREAD position will NOT be initialized to the
  SQL_THREAD position,
- SQL_THREAD position will NOT be initialized to the new
  relay log.

It looks like, when the SQL_THREAD does not have a
Relay_Master_Log_File, relay_log_recovery does not work.

Analysis:
========
When relay-log-recovery is set existing relay logs are
ignored and IO_THREAD positions will be initialized to
SQL_THREAD's positions and SQL_THREAD positions will be set
to newly generated relay log. The old relay logs will be
purged by the normal purge mechanism. There can be a special
case where sql thread has never started all, in such case
SQL_THREAD's positions will not be initialized. Existing
recovery mechanism is tightly coupled with
Relay_Master_Log_File's value if the file name is not set
recovery will not happen.

Fix:
===
During recovery if Relay_Master_Log_File is not set open the
relaylog index file. Read the relay logs from the first
relay log parse each of these files and look for Rotate
event from the master which will specify from where
replication has started. Extract master_log_file and
master_log_pos from master's rotate event and set it as
SQL_THREAD's Relay_Master_Log_File and position.