Issue #1908194 by  richard.c.allen2386: Document what happens in drupal_get_path if the file is not found
Issue #1908192 by mitron: Document what happens in drupal_get_filename() if the file is not found
Issue #1852288 by underq, aaronott, YesCT, heyrocker, Gábor Hojtsy: Update documentation to namespace standards