Bug 25040: monkeypatch Schema::Loader for recent MariaDB

Bug 25040: monkeypatch Schema::Loader for recent MariaDB

Recent versions of MariaDB changed the output of 'DESCRIBE' for
timestamp columns with defaults from `CURRENT_TIMESTAMP` to
`current_timestamp()`.  As such the code inside
DBIx::Class::Schema::Loader which catches such cases and outputs
`\"current_timestamp"` as a sensible cross platform default is missed
and this leads of inconsistent class files and bugs with out default
lookup code in Koha::Objects.

This patch serves as a backport of the code I have submitted upstream
such that out developers can continue to use update_dbix_class_files.pl
to build their schema classes from the database and regardless of their
db server version get a consistently correct output.

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Joy Nelson <joy@bywatersolutions.com>