escaped field names

When in mixed or statement mode, the master logs LOAD DATA
queries by resorting to an Execute_load_query_log_event. This
event does not contain the original query, but a rewritten
version of it, which includes the table field names. However, the
rewrite does not escape the field names. If these names match a
reserved keyword, then the slave will stop with a syntax error
when executing the event.

We fix this by escaping the fields names as it happens already
for the table name.

mysql-test/extra/rpl_tests/rpl_loaddata.test:
  Added test case for the reported bug.
mysql-test/r/mysqlbinlog.result:
  Changed result to support escaped field name.
mysql-test/suite/binlog/r/binlog_killed_simulate.result:
  Changed result to support escaped field name.
mysql-test/suite/binlog/r/binlog_row_mix_innodb_myisam.result:
  Changed result to support escaped field name.
mysql-test/suite/binlog/r/binlog_stm_blackhole.result:
  Changed result to support escaped field name.
mysql-test/suite/binlog/r/binlog_stm_mix_innodb_myisam.result:
  Changed result to support escaped field name.
mysql-test/suite/rpl/r/rpl_innodb_mixed_dml.result:
  Changed result to support escaped field name.
mysql-test/suite/rpl/r/rpl_loaddata.result:
  Added result for new test. 
  Changed show slave status positions which are now different because of
  extra escape character in field names.
mysql-test/suite/rpl/r/rpl_loaddata_fatal.result:
  Changed show slave status positions which are now different because of
  extra escape character.
mysql-test/suite/rpl/r/rpl_loaddata_map.result:
  Changed result to support escaped field name.
mysql-test/suite/rpl/r/rpl_stm_log.result:
  Changed result to support escaped field name.
mysql-test/t/mysqlbinlog.test:
  Changed positions which is now different because of extra escape 
  character in field names.
sql/sql_load.cc:
  Appended escape characters before and after field names.