latest changes, revert at will.

examples/dg.ufl

examples/mixed.ufl

examples/stokes2d.ufl

python/dune/perftool/compile.py

python/dune/perftool/file.py

python/dune/perftool/loopy/transformer.py

python/dune/perftool/pdelab/localoperator.py

python/dune/perftool/ufl/transformations/__init__.py

...erftool/ufl/transformations/extract_accumulation_terms.py

python/dune/perftool/ufl/transformations/indexpushdown.py

python/dune/perftool/ufl/transformations/reindexing.py

python/ufl