Trying to understand the TestHelp.py failure from 6c089b2a.

Sadly, the test passes on macOS, but fails on Ubuntu & Win.  The
extra option printing is supposed to be suppressed by the return
from CommandObjectAlias::IsDashDashCommand.  That was changed, but just
by replacing an inline string compare with a const string from
CommandInterpreter.  Putting the old version back temporarily to
see if that is really the problem.