When following error message is shown, then it will get converted to the
correct Exception classs of NotNullConstraintViolationException:

  PDOException: SQLSTATE[HY000]: General error: 1364 Field '...' doesn't have a
  default value

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