Segregated support of unique index and unique constraint. Added missing commits: 400d73c8a1e4f53459a877c8652811ee22c0913b, e91811cb3fe3101d7d8ac95c45f8bc1ba9bd913a, a4ecf053186b11bc31fbff79ef36248500383908, d7d1c397a35735383b34632d3a67bbc3a3371a45, c71b3ae0425e5c039b047825dbf8351a773e6785, 2f9da39ec645b54d08c95649c99d7b87a32bdc72 and 9aa4e79aab0477b4212b01d65de53193d9559e39

Removed the `Dbal` prefix from the class names and moved them to the `Doctrine\Tests\DBAL` namespace.

The method is not used for anything else than skipping tests for specific drivers. Cross-driver portability should be established by drivers, not outside of them based on their name.

1. SchemaManagerFunctionalTestCase can be run only via an extending class. Otherwise, it skips all tests. If the test case is represented as an abstract class, PhpStorm will offer a choise of concrete classes which is very handy when debugging test failures.
2. DbalFunctionalTestCase and DbalPerformanceTestCase are meant to be used as base classes and don't contain any tests.

This reverts commit e3ab1276, reversing
changes made to f988b0a6.

I am not sure if there is a rationale behind ignoring extra keys like
this. I was under the impression that something might copy options to
platform specific options, thus leaving options in the original array,
knowing they would be ignored anyway. If it is the case, it would be
best to just move them, otherwise, this commit might help troubleshoot
some mapping issues.
I had to fix some tests that wrongly used that options array (maybe
these options were valid at some point?).