CoreStringUtils::RemoveLines: Fix bug that left out the last endl from the file.
Improve logic and code to support defining a renderer for --headless runs. If you want to override this config for a --headless run use the --opengl and --direct3d9 params. Fix 'Null' to 'NULL' in the --nullrenderer plugin name, this caused this plugin to not load at all and went to the dx/opengl fallbacks.
Fix code around Tundra to work without crashing when a null/headless renderer is used.