Improve qb validation

fixes some bugs in the tests, also fixes https://github.com/doctrine/phpcr-odm/issues/541

note ``Doctrine\Tests\ODM\PHPCR\Query\Builder\BuilderConverterPhpcrTest::testOrderBy`` is failing .. but honestly I don't really think such a test makes sense. It is way too complex to test as it requires so much mocking. IMHO we are better off testing this via the various existing functional test. So I vote for removing that test.

/cc @dantleech 

So by having this here we also prevent:

````
$qb->where()->eq()->field('a.nodenamefield')->literal('foo');
````

because the user should be doing

````
$qb->where()->eq()->localname('a')->literal('foo');
````

I think.