Get Composer to find the dev dependency for symfony-console-completion.
Second attempt
Update composer.lock
Third attempt
Updating/installing via 'require' is broken.

Needs a new tagged version of symfony-console-completion. This Composer issue
is the problem: https://github.com/composer/composer/issues/3367
Improve error if the autoload.php is not present.
Test on PHP 5.3
Update console completion dependency, now tagged as stable upstream.
Re-enable exceptions when getting environments.

Need to find some other way to handle exceptions during auto-completion.
Simplify asking confirm questions.
Release v1.3.0
Remove excess semicolons.
drush version -> drush --version

See issue #160
Hide the completion command in the list.