Fix up options parsing
Fix up options parsing

Always recognize the standard "--" argument to indicate "end of
options".  Otherwise fscryptctl can't operate on files that are
literally named "-h", "-v", "--help", or "--version".

Recognize "--" even for commands that don't currently take options, and
moreover, reject unknown options in such commands.  Otherwise the
fscryptctl commands work inconsistently, and later adding options to
commands that don't currently take options would be a breaking change.

google/fscryptctl,google/fscryptctl