Add unit tests for existing runfile recognition.

In order to extend the recognition of runfiles, tests need to be added
before any code change. PHPUnit and vfsStream have been chosen as tools
for this task and added as dev-requirement through composer.

The existing runfile name tests are located in test/phake/test folder,
which is written into composers PSR-0-compliant autoloader section.

PHPUnit configuration is straightforward and just bootstraps composers
autoloader.
Support lowercased phakefile filenames.

Support lowercased runfiles to be recognized as well. Example:

    phakefile
    phakefile.php

Tests for proper file recognition added aside.