Update phpunit to 4.x.
Remove unnecessary arguments to composer install.

We don't set these elsewhere and don't need to set them here.
Fix indentation in phpunit.xml.
Specify test suite in phpunit.xml.
Use PHPUnit as a library.
Restrict codesniffer to 1.4.x.

1.5 was backwards breaking from our standpoint here.  At some point we
need to update it, but that is not a simple change.