corruption on ADD PARTITION and LOCK TABLE
Bug#53770: Server crash at handler.cc:2076 on
           LOAD DATA after timed out COALESCE PARTITION

5.5 fix for:
Bug#51042: REORGANIZE PARTITION can leave table in an
           inconsistent state in case of crash
Needs to be back-ported to 5.1

5.5 fix for:
Bug#50418: DROP PARTITION does not interact with
           transactions

Main problem was non-persistent operations done
before meta-data lock was taken (53770+53676).
And 53676 needed to keep the table/partitions opened and locked
while copying the data to the new partitions.

Also added thorough tests to spot some additional bugs
in the ddl_log code, which could result in bad state
between the .frm and partitions.

Collapsed patch, includes all fixes required from the reviewers.