The `PostgreSqlPlatform`, `SQLAnywherePlatform` and `SQLServerPlatform` classes have been renamed to `PostgreSQL94Platform`, `SQLAnywhere16Platform` and `SQLServer2012Platform` respectively.

When deprecating an old platform version, we can deprecate and later remove a specific class. Otherwise, there's no way to express the deprecation on the class level and the upgrade notes contain sentences like: "`XYZPlatform` and `XYZKeywords` now represent XYZ (version)".

Support for Partial Indexes was available in Doctrine 1 following
http://www.doctrine-project.org/jira/browse/DC-82. This commit
reintroduce support for Doctrine 2. We use the same syntax with an
optionnal "where" attribute for Index and UniqueConstraint.

- added test for getListTableColumnsSQL
- added test for getListTableForeignKeysSQL
- added test for getListTableIndexesSQL

DBAL-54 was fixed in commit 3d55dc8e by
changing SQL queries order. However it was later reintroduced.

This patch uses a different, more future-proof way, approach by using
DROP SEQUENCE ... CASCADE syntax, and thus does not depend on queries order.

[DBAL-374] Fix issue with column quoting in primary keys, fixing this in indexes in general is much more complex as the code is messy.