FULL TABLE REBUILD

Analysis:
--------
Certain ALTER TABLE operations on tables with temporal columns
in pre-5.6.4 binary format were forced to use 'slow' COPY
algorithm, even though in theory such operations could have
been executed using 'fast' INPLACE algorithm. Thus for large
tables such ALTER TABLEs took a lot of time while they were
expected to be 'fast'.

Starting from version 5.6.16, ALTER TABLE statements with
ADD/CHANGE/MODIFY COLUMN, ADD INDEX or FORCE clauses upgrades
the temporal columns in the old binary format to the new format
introduced in version 5.6.4. Such upgrade requires table
rebuild using COPY algorithm and hence it is not a 'fast'
operation, as it can be expected in some cases
(for example, when adding elements to the end of enum type).

Fix:
---
1) A new global dynamic variable 'avoid_temporal_upgrade'
   and corresponding start-up option is introduced.
   Values accepted: Boolean values.
   Default value: 0 or FALSE.
   Note: The variable/option is deprecated and will be removed
   in the future release.

   When the variable is set to 1, ALTER TABLE will not try to upgrade
   the old temporal columns (unless temporal column definition
   is changed). Thus the ALTER TABLE will behave in the same way
   as it did in MySQL-5.6.15.

   When the variable is set to 0, ALTER TABLE will try to upgrade
   old temporal columns to new format for ALTER TABLE requests
   ADD/CHANGE/MODIFY COLUMN, ADD INDEX or FORCE operation i.e the
   behavior introduced from MySQL-5.6.16.

2) Also a new per-session dynamic system variable
  'show_old_temporals' and a corresponding start-up option is
   introduced.
   Values accepted: Boolean values.
   Default value: 0 or FALSE.
   Note: The variable/option is deprecated and will be removed
   When this variable set to 1 for the session, SHOW CREATE
   TABLE behavior for that session is changed to mark temporal
   columns using old binary format in the following way:

   CREATE TABLE `ts` (
   `t` timestamp /* 5.5 binary format */ NULL DEFAULT NULL
   ) ENGINE=InnoDB DEFAULT CHARSET=latin1
   Also a similar comment is added to the COLUMN_TYPE field of
   I_S.COLUMNS table.

   When this variable is set to 0, both SHOW CREATE TABLE and
   I_S.COLUMNS won't mark the old temporals and continue with
   the existing behavior.