Dirty fix for issue with parent constraint

This fixes the problems with the failing doctrine_dbal tests, however I'm pretty sure that other things are broken here (e.g. the same problem should happen with walkDescendentNodeConstraint)

The issue is that ``$contraint->getParentPath`` returns ``"/functional/"`` (i.e. it returns the double quotation marks in addition to /functional/). I think this would be an issue with ``Sql2ToQomConverter``, in that it retains the quotation marks. However this works for the jackrabbit transport.

So where is the fault? Should ``Sql2ToQomConverter`` retain the quaotation marks, or should jackalope/doctrine-dbal remove them?