Add PSR-4 class loader. (tests needed)
PSR-4 class loader: Add getters for PSR-4 prefixes. Rename PSR-0 related attributes by appending *Psr0. Add more comments.
PSR-4 loader: Fix comments: PSR-0 related methods should have comments refering to PSR-0 and prefixes. PSR-4 related methods should have comments refering to PSR-4 and namespaces.
Further improve comments.
PSR-4 ClassLoader: Bug fix: PEAR-like path needs ".php" appended.
Add unit tests for ClassLoader, covering PSR-0 and PSR-4.
AutoloadGenerator to support PSR-4. Tests included.
Travis CI should use bin/composer and not system-wide Composer.
run system-wide composer install and THEN run bin/composer install
Add psr-4 stuff in a few more places.
Validation to make the combination of target-dir with psr-4 illegal.
expected message in ValidatingArrayLoaderTest should also  contain psr-4 as allowed key.
phar compiler should also compile autoload_psr4.php
Verify generation of autoload_psr4.php even if empty.
Fix indentation of  assignment in AutoloadGeneratorTest
More interesting generator tests for PSR-4.
ConfigValidator: ensure that require-dev exists during override check

- Ensure that require-dev is present before checking for dependeny overrides.
- A small grammar update for the warning message.
Fix indenting, refs #2535
Fix uninitialized var, fixes #2539
Handle metapackages properly in downloadmanager, fixes #2466