Plugin store requires cleaner composer.json than Composer at dev src

Description

If you happen to have a composer.json repository definition of file type whose location no longer exists, loading another plugin from the Store will fail, mentioning this lack, though it doesn't using Composer directly from dev.

Workaround: remove the irrelevant repository definition from original composer.json."
Or: composer require newplugin at source, without removing the definitiion, as this will work

Conclusion: Craft Plugin Store operations are somehow more stringent than ordinary Composer; may want to see if that's necessary

Steps to reproduce

1. Have a file path repository definition in composer.json, such as for a plugin not yet on Packagist that you wanted to try.
2. But don't have the plugin at the path any more
3. Attempt to use the Plugin Store to add anorher plugin
4. Soon fails, with e.g. Error: No driver found to handle VCS repository plugins/craft-neo Output: Loading composer repositories with package information Error: No driver found to handle VCS repository plugins/craft-neo Output: Loading composer repositories with package information
5. Remove the unused file path repository from composer.json and upload it -- now Plugin Store will successfully load a new plugin, such as CkEditor
6. Alternatively, leave the file path repo in, and require the new plugin at dev src -- this will work, and you can upload composer.json plus composer.lock to let Craft install to be up-to-date

Additional info

PHP version 7.1.7-1+ubuntu16.04.1+deb.sury.org+1
Database driver & version MySQL 5.7.19-0ubuntu0.16.04.1
Image driver & version GD 7.1.7-1+ubuntu16.04.1+deb.sury.org+1
Craft edition & version Craft Personal 3.0.0-RC1
Yii version 2.0.13.1
Twig version 2.4.4
Guzzle version 6.2.1
Imagine version 0.7-dev
Plugins: yes