CLI: fix a parser bug

Make the Or token try to match all of its alternatives unless one of them
matches the full command line. When there are several matches, the one that
consumes the most input is chosen. Ties are broken by choosing the 1st match.

Fixes: MN-281

Signed-off-by: Guillermo Ontanon <guillermo@midokura.jp>
Merge pull request #55 from gontanon/parserBug

CLI: fix a parser bug