[A] PD: Parse output section; Add output_file_prefix.
Pass output file prefix to Process::post().
[PL] GW: Add output in post().
md pass output stream to post().
md rewrite post();
DEBUG_ALL
Merge branch 'SimulationOutput' into develop
Make AddTest::PATH relative.

The new AddTest_SOURCE_PATH includes the
ExternalData_SOURCE_ROOT in AddTest.cmake.
Use AddTest_BINARY_PATH for simulation result file.

Used in the diff tester.
Merge branch 'test-improvements' into develop