This is not actually necessary. Adding a handler for std::exception also
hid the more specialized handlers provided by pybind11 itself.

[lapacke] fix error in previous commit

refs https://github.com/dune-community/Dockerfiles/pull/19

[lapacke] add dgeevx, use new macro to silence "unused variable" warn…

Allow for std::string in the python bindings for FieldVector and FieldMatrix.
Required for python bindings for ExpressionFunction.

[cmake] exclude builder_definitions.cmake from cmake-format

Minor changes

Fix FindMKL, search for clang-format-3.9

Some cmake changes

Some fixes for new PerThreadValue for clang and dune-gdt

- see https://gcc.gnu.org/gcc-6/porting_to.html#overloaded-abs

Rebase PerThreadValue on tbb::enumerable_thread_specific