names in replicated statements

BUG#50653: drop procedure implicitely treats db name in a case
           sensitive way
      
This bug revealed itself while using case sensitive filesystems
and exhibited two symptoms:
      
  1. If setting lower_case_table_names=1 on the slave, but not on
     the master, this setting will not convert database name in
     replicated statements, ultimately breaking replication;
      
  2. The same problem for symptom 1. surfaced in RBR, but this
     time for table names, as these would not be converted to
     lower case for row based replication events.
      
Symptom 1. is addressed by conditionally converting to lower
case, database name on Query_log_event constructor and
Load_log_event::do_apply_event.
      
Symptom 2. is addressed by conditionally converting to lower
database name and table name when processing Table_map_log_event.

A side note on BUG#50653. It's basically a duplicate of BUG#37656
but I included a test case for it in this patch.