the problem was that the search for the periodic neighbour deletes the periodic
boundary faces from the boundary and the elements get oriented between insertion
and this. So it does not find the elements. Now the search is done after the recreation of
the boundaryIds with respect to the new element orientation

[bugfix] include missing header



See merge request !5

Remove dereference of Entity; fix misleading indentation.

GCC with -Wall will warn about the latter.

See merge request !6

GCC with -Wall will warn about the latter.

Use <array> instead of <dune/common/array>

Please see also core/dune-common#13.

See merge request !4

Addendum to C++11-type-traits switch.

This is an addendum to !2.

See merge request !3

For std::conditional

Feature/use cxx11 type traits

Use std::conditional and std::remove_const

See merge request !2