WL#5818: Create interface for writing LOAD DATA to binary log

This is a step towards making replication a library, such that the 5.6 rpl-
lib can be plugged into the 5.5 core [WL#5675].

In this WL, we add an interface for writing LOAD DATA INFILE statements to the 
binary log.

TODO: design this.

 - In sql_load.cc it creates a Delete_file_log_event and an
   Execute_load_query_log_event. We need to add an interface for that to
   rpl-lib.

 - In sql_load.cc, it creates a Load_query_log_event. This is only used to
   generate a LOAD DATA INFILE query that will be passed to
   Execute_load_query_log_event. Very strange. We should get rid of the
   Load_query_log_event and use rpl-lib's interface for
   Execute_load_query_log_event instead.