Re #6804. Add a missing test.
Re #6804. Remedy cppcheck warnings.
Re #6804. Remove unused variables and thus warning.
Re #6804. Remove strange categorization.
Re #6804. cppcheck warning.
Re #6804. Remove a comment that I don't want to see every time.
Re #6804. Fix indentation. No code changes.
Re #6804. Remove unused variable.
Re #6804. Remove deprecated header and its usage.
Re #6804. MSVC compiler warning.
Re #6804. MSVC compiler warning.
Re #6804. MSVC compiler warning.
Re #6804. MSVC compiler warning.
Re #6804. MSVC compiler warning.
Re #6804. MSVC compiler warnings.

Reordering the headers leads to the suppression of warning C4251 getting
picked up from System.h via Algorithm.h
Re #6804. Remove unjustified warning suppression.

This caused an unrecognized pragma warning with the Intel compiler and
is not how we deal with warnings anyway except as a last resort.
Merge branch 'feature/6804_warnings' into develop