Add clear cache command.
Fix typo in src/Composer/Command/ClearCacheCommand.php
Clean up unused 'use' statements
Merge pull request #3034 from Petah/clear-cache

Add clear cache command.
Initial commit to add a command that moves Composer into a global directory

This intention is to also use this from within the command script, with
slightly different input/output so that the user-experience when using
the installer is really good (--install-mode).
Only run this command when we're *not* on Windows