This doesn't change the automatic command finder, so it really only helps
increase match hit rate in case of low confidence level delta between the 2 top
hits. For example, given commands 'set-commit' and 'dcommit', a user typing
'set_commit' would hit:
- 'set-commit': 90%
- 'dcommit': 70.5%

Since subcommand.py uses a 30% minimum confidence level between the two top hit
to automatically select a command, it will err on the side of safety and will
abort instead of selecting 'set-commit'.

This change fixes this specific case but won't trigger on partial matches, e.g.
'set_commi' for 'set-commit'.

R=stip@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1066923003

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@294700 0039d316-1c4b-4281-b951-d872f2087c98