Current auto increment value is placed in partition in which latest
record was saved. So to get auto_increment they have to scan
all partitions and return max value.


mysql-test/r/partition.result:
  Fix for bug#18753 Partitions: auto_increment fails
  test case
mysql-test/t/partition.test:
  Fix for bug#18753 Partitions: auto_increment fails
  test case