Problem:
=======
when the binlog_row_image is FULL, we set read_set and
write_set all before update. This leads to setting
used_key_is_modified true, which lead to mysql_update use
temporary at last. Actually there is no need to use
temporary in most cases. The root cause is that we set
read_set and write_set too early.

Analysis:
=========
As reported in problem description table's read_set and
write_set are set earlier.
'mark_columns_per_binlog_row_image' is the function call
which sets these read and write sets. But this is called
at an earlier stage during execution and in the case of
binlog_row_image=FULL it will set all the bits of read and
write sets. This will make the update query to think that
a key is being modified by the existing update query. Even
though it is not modifying the key field. This will force
the update query to use a temporary table even though it may
not be required. The same problem exists even in the case of
binlog_row_image=NOBLOB. This problem is specific to single
table updates.

This issue is not present in the case of multi table update.
As in the multi table update case, the check for 'used key
is modified or not' is done before marking
read_set/write_set as per binlog_row_image. Hence binary log
specific bits are not influencing query to use temporary
table.

Fix:
===
Implemented single table update to follow the same mechanism
that multi table update follows. i.e Mark the columns in
table's read_set/write_set as the binlog_row_image after the
'used key is modified or not' decision is taken.