Add test to ensure renamed or removed columns that reference removed tables have their FK constraints properly removed.

Added parameter "default_dbname" to pdo_pgsql driver which can be used to override the default database

cover in test suite that platform throws exception on generating inline column comment SQL if unsupported

fixes #1206

also refactors URL path evaluation into smaller methods

fixes #1106

fixes #2252

fixes #2270

fix usage of PDO::PGSQL_ATTR_DISABLE_PREPARES for pdo_pgsql extension setups not built from PHP core

fixes #2249

fixes #1339
closes #921

Use shorter table names - Oracle allows max 30 characters - http://docs.oracle.com/cd/B19306_01/server.102/b14200/sql_elements008.htm#sthref723