--FLUSH-LOG BREAKS CONSISTENCY

The transaction started by mysqldump gets committed
implicitly when flush-log is specified along with
single-transaction option, and hence can break
consistency.

This is because, COM_REFRESH is executed in order
to flush logs and starting from 5.5 this command
performs an implicit commit.

Fixed by making sure that COM_REFRESH is executed
before the transaction has started and not after it.

Note : This patch triggers following behavioral
       changes in mysqldump :

1) After this patch we no longer flush logs before
   dumping each database if --single-transaction
   option is given like it was done before (in the
   absence of --lock-all-tables and --master-data
   options).

2) Also, after this patch, we start acquiring
   FTWRL before flushing logs in cases when only
   --single-transaction and --flush-logs are given.
   It becomes safe to use mysqldump with these two
   options and without --master-data parameter for
   backups.


client/mysqldump.c:
  Bug#12809202 61854: MYSQLDUMP --SINGLE-TRANSACTION
               --FLUSH-LOG BREAKS CONSISTENCY
  
  Added logic to make sure that, if flush-log option
  is specified, mysql_refresh() is never executed after
  the transaction has started.
  
  Added verbose messages for all the executions of
  mysql_refresh() in order to track its invocation.
mysql-test/r/mysqldump.result:
  Added test case for Bug#12809202.
mysql-test/t/mysqldump.test:
  Added test case for Bug#12809202.