Try -Wextra for maximal paranoia

- add missing newlines at EOF
- ignore installed libs (like openmpi) and their warnings with
  -Wno-system-headers
- cmake:
  - include HDF5 and MPI as SYSTEM pathes to avoid checking their headers
    with our paranoid -Wextra -Werror settings
  - version 2.8.5+ will be needed to set the system include flag -isystem right
    on all systems and for c libs
Remove unused-parameters in ParallelDataCollector

- well, they hint an unused interface, but I just removed their
  variables