update accross partitions.
      
It's not Innodb-specific bug.
ha_partition::update_row() didn't set
table->timestamp_field_type= TIMESTAMP_NO_AUTO_SET when
orig_timestamp_type == TIMESTAMP_AUTO_SET_ON_INSERT.

So that a partition sets the timestamp field when a record
is moved to a different partition.

Fixed by doing '= TIMESTAMP_NO_AUTO_SET' unconditionally.
Also ha_partition::write_row() is fixed in same way as now
Field_timestamp::set() is called twice in SET_ON_INSERT case.

(Chad queues this patch on demand by Trudy/Davi.)