[FIX] Allow to use ManyToMany with all operators

Hi,

ping @guillhermoblanco : I think this may be blocking for 2.5

I introduced not so long ago support for ManyToMany for Criteria. However, I realized my implementation was really incomplete, because I hard-coded the "=" operator (https://github.com/doctrine/doctrine2/pull/885/files#diff-982b7374bbe9d5f4b6b71f4869a446eaR575). This means that it fails in a lot of cases when you use something different than "eq" for Criteria.

This PR fixes that, however it's a bit hacky. The SqlExpressionVisitor was made by type hinting for a BasicEntityPersister, preventing us from using us for a collection persister. Therefore I added a new interface to keep BC.

There is also a lot of code duplication (the whole "getSelectConditionSQL" was copied from the BasicEntityPersister), but without trait or BC, I have no idea about how to solve it.

All tests pass, test were added for other operators.