That was a bad idea from the beginning! It lead to a situation,
where calls from within a generator inherited their context tags.
Should be fixed now.

Conflicts:
	python/dune/perftool/pdelab/quadrature.py

Stage instructions are not the solution.

We previously completely avoided loopy for temporary declaration.
We now rely on it again, but have DuneTemporaryVariable, which is
capable of doing a bit more things (and at the same time handles
the indexing question)

* Enable backend functions which are *not* generators
* Use the sumfac switch as a default switch

Needs a small fix in loopy (MR opened).

It is a memory reinterpretation

... instead of reimplementing it all over the place