Add full support for auto-initialized/updated timestamp and datetime

The task is to extract and backport all changes from MySQL 5.6 that move timestamp handling from the handler interface to the server.

The change was done by:
revno: 3402.50.105
committer: Martin Hansson <martin.hansson@oracle.com>
branch nick: mysql-wl5874-push
timestamp: Tue 2012-01-31 16:16:16 +0100
message:
WL#5874: CURRENT_TIMESTAMP as DEFAULT for DATETIME columns.

There is no public WL, however there is documentation:
http://dev.mysql.com/doc/refman/5.6/en/timestamp-initialization.html

First goal is to evaluate MySQL's patch, whether it makes sense to backport it, or to reimplement it.
Specifically check what are the changes to the FRM format, so that we can read MySQL 5.6 FRM files.

Additional patches to investigate:
Bug#11745578: 17392: ALTER TABLE ADD COLUMN TIMESTAMP
DEFAULT CURRENT_TIMESTAMP INSERTS ZERO

Possibly the following patch is related:
committer: Martin Hansson <martin.hansson@oracle.com>
branch nick: mysql-trunk-security
timestamp: Thu 2012-02-09 13:33:22 +0100
message:
Merge of fix for Bug#11765810.

In addition, MySQL 5.6.6 adds the following system variable, and corresponding change in behavior:
http://dev.mysql.com/doc/refman/5.6/en/server-system-variables.html#sysvar_explicit_defaults_for_timestamp

Since MySQL 5.6.6 is not Launchpad yet, it seems that the above is implemented by the following patches:

• http://lists.mysql.com/commits/144203?f=plain
• http://lists.mysql.com/commits/144281?f=plain
• http://web.archiveorange.com/archive/v/BCyfsTLtQJJmNDcTMHWh
• http://web.archiveorange.com/archive/v/BCyfsJyvYzyNAUfJpvDI