I extended the task to cleaning error messages, making them look nicer,
and making the output of SHOW SLAVE STATUS (column Last_error) be as complete
as what's printed on the .err file;
previously we would have, for a failure of a replicated LOAD DATA INFILE:
- in the .err, 2 lines:
"duplicate entry 2708 for key 1"
"failed loading SQL_LOAD-5-2-2.info"
- and in SHOW SLAVE STATUS, only:
"failed loading SQL_LOAD-5-2-2.info".
Now SHOW SLAVE STATUS will contain the concatenation of the 2 messages.


sql/log_event.cc:
  Print the default database when replication stops because of an error. Previously, we had:
  "error "Duplicate entry 87987 for key 1", query 'insert into t values(87987)'", ie the db
  was not mentioned, making it hard for cases where the same table name is used in
  several databases.
  Lengthened some error messages (for failing replication of LOAD DATA: mention the table
  and the db).
  Changes so that SHOW SLAVE STATUS reports as complete errors as the .err file.
sql/slave.cc:
  Removed a useless declaration (the rewrite_db() function is already declared in slave.h).
  Added missing ')' in error messages.
  Tried to make error messages look nicer (previously we had
  "do START SLAVE;, error_code=1062"
  now we'll have
  "do START SLAVE; . Error_code=1062".
  This form has been discussed, I agree it's no panacea, but it's still more readable
  like this. To be improved in the future :)
sql/slave.h:
  declarations.