Ignore unknown options in DH_OPTIONS. Debhelper will always ignore such options,...

Ignore unknown options in DH_OPTIONS. Debhelper will always ignore such options, even when unknown command-line options are converted back to an error. This allows (ab)using DH_OPTIONS to pass command-specific options. (Note that getopt will warn about such unknown options. Eliminating this warning without reimplementing much of Getopt::Long wasn't practical.)