ADOdb pgsql fix: AlterColumnSQL conversion from bool to int

When changing type of a column from boolean to integer, PostgreSQL does
not provide implicit type cast, so the library needs to specify it via
USING statement when generating the SQL·

Porting part b) of commit 10871e5afc0bffc546b1a3d60bd7a459fa37e762

This issue exists in ADOdb <= 5.17. Upstream bug report
http://phplens.com/lens/lensforum/msgs.php?id=19204

Fixes 0014398