Fix quoting conventions for Twitter commands.

Two bugs here:

1. The documentation incorrectly implies that arguments can be
omitted, when really the argument parser is much dumber than that.
If there are two optional arguments, you can't omit the first one
and give the second one; that's ambiguous.

2. There is a codepath for replycmd when status_id is not set
(this should be impossible) which passed wrong arguments.

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>