Problem:

The function row_upd_changes_ord_field_binary() is used to decide whether to
use row_upd_clust_rec_by_insert() or row_upd_clust_rec().  The function
row_upd_changes_ord_field_binary() does not make use of charset information.
Based on binary comparison it decides that r1 and r2 differ in their ordering
fields.

In the function row_upd_clust_rec_by_insert(), an update is done by delete +
insert.  These operations internally make use of cmp_dtuple_rec_with_match()
to compare records r1 and r2.  This comparison takes place with the use of
charset information.

This means that it is possible for the deleted record to be reused in the
subsequent insert.  In the given scenario, the characters 'a' and 'A' are
considered equal in the my_charset_latin1.  When this happens, the ownership
information of externally stored blobs are not correctly handled.

Solution:

When an update is done by delete followed by insert, disown the relevant
externally stored fields during the delete marking itself (within the same
mtr).  If the insert succeeds, then nothing with respect to blob ownership
needs to be done.  If the insert fails, then the disown done earlier will be
removed when the operation is rolled back.

rb#4479 approved by Marko.