Fix regression, likely caused by me, where DIR /O options entered at the command line do not override any /O options that might be set in the DIRCMD environment variable. Fix is to reset applicable sort order state whenever /O is encountered in the options list.
-- v3: cmd: Allow DIR /Oxxx at the command line to override DIRCMD=/Oyyy set in the environment. cmd/tests: Duplicate DIR /O tests, but specify parameters via DIRCMD environment variable.