Support alternate names for composer files

[pombredanne]

See for instance

• https://raw.githubusercontent.com/petrknap/trunk/ae09c1f0b4aeb16685614657fb9cf0bde9dcce57/symfony.composer.json
• https://raw.githubusercontent.com/xrowgmbh/xrowvagrant/70a3b29ecba5cf3781ce11962c2b4585ef009b13/ezcluster/templates/composer.symfony.json
• https://github.com/petrknap/trunk/blob/ae09c1f0b4aeb16685614657fb9cf0bde9dcce57/php.composer.json

The same name pattern is likely there for the generated companion lockfile.

We should relax patterns and accept filename such as /[^/]*composer.json, /composer[^/]*.json, and the same for lockfiles.