but the statement is written to binlog

TRUNCATE PARTITION was written to the binlog
even if it failed before calling any partition's
truncate function.

Solved by adding an argument to truncate_partition,
to flag if it should be written to the binlog or not.

It should be written to the binlog when a call to any
partitions truncate function is done.

mysql-test/r/partition_binlog.result:
  New result file
mysql-test/t/partition_binlog.test:
  New test file, including DROP PARTITION binlog test
sql/ha_partition.cc:
  Added argument to avoid binlogging failed truncate_partition that
  have not yet changed any data.
sql/ha_partition.h:
  Added argument to avoid excessive binlogging
sql/sql_partition_admin.cc:
  Avoid to binlog TRUNCATE PARTITION if it fails before
  any partition has tried to truncate.