This patch provides a new mode FULL_NODUP to binlog_row_image system
variable. With FULL_NODUP mode, all columns are included in before
image, but only updated columns are included in after image for UPDATE.
While all columns are included in the after image for INSERT.
FULL_NODUP is for replacing FULL mode. It includes all data of
the before and after image as FULL mode, but it uses less storage
especially in the case that only a few columns are updated.
Note: It will binlog full before and after image for all modes if the
table has no primary key. FULL_NODUP follows the behavior.
