Make SimpleOptions parser more strict
Summary: We're over-generous in accepting options right now, see T876.
Test Plan: Typed out the repro case in T867, got an initial "select ..." line
instead of a codeblock named "1"; updated unit tests.
Reviewers: btrahan, viyer
Reviewed By: viyer
CC: aran, epriestley
Maniphest Tasks: T876
Differential Revision: https://secure.phabricator.com/D1623