Detailed revision comments:

r6789 | jyang | 2010-03-10 11:18:18 +0200 (Wed, 10 Mar 2010) | 10 lines
branches/zip: If a unique index is on a column prefix, such
unique index cannot be upgrade to primary index even if there
is no primary index already defined. Also fix possible corruption
when initialize "ref_length" value in case there is a mismatch
between MySQL and InnoDB primary key. Fix bug #51378: "Init
'ref_length'  to correct value, in case an out of bound MySQL
primary_key".
rb://262 approved by Marko.