Test for issue #910

Test for issue #910.

Projections_DuplicateColumns demonstrates the issue.
Projections_DuplicateColumns demonstrates a fix. I added the fixed Query class (FixedJPASQLQuery) as an inner class for convenience.

This obviously isn't production quality code and cannot be merged; I just mean to finger-point the issue.

Note that while the use case seems nonsensical, it actually can happen when using a `QueryProjection` multiple times with only some parameters that differ, and then combining them as parameters of a single, different projection. For instance:
```
new QSuperProjection(
  new QProjection(a.count(), b.count()),
  new QProjection(a.count, c.count())
);
```