[CMake] add -DENABLE_ALUGRID to ALL_PKG_FLAGS if ALUGrid is found
remove warning: comparison between signed and unsigned integer expressions
Deprecated ALUGrid. Use DUNE-ALUGrid instead.
remove warning.
[dgf] remove unused include

Historically, the dgf entity key depended on ALUGrid's element
numbering. Since the introduction of the grid factory, this is no longer
the case. However, there was a left-over include to ALUGrid's topology
mapping, which causes trouble in combination with dune-alugrid. This
patch removes this unused include.
Merge branch 'master' into p/dominic/all-entities-yaspgrid