* Autoloader infinite recursion fix

Fixes simplesamlphp/simplesamlphp#1030

* Added test to ensure old autoloader behaviour is preserved

Also fixed undefined variable notice

Since the class cannot be named "Const" when using namespaces, due to "const" being a reserved word, we needed to rename the class. That requires also some logic in the autoloader to map the old name to the new one.

Doing so allows us to mock the class. Otherwise, the _autoload_module.php is always called first, and when it tries to register the functions from that class, it automatically autoloads it, making it impossible to mock it afterwards.

The 2.x branch of XMLSecLibs uses namespaces, so we need to make sure we can still load the XMLSec* classes after updating the dependency. We can do that in the autoloader, looking for the classes with namespaces, and creating class aliases.

Migrate the logout handlers to namespaces, change the base abstract class to be an interface instead.

Migrate all the logging handlers to namespaces. Make SimpleSAML\Logger a bit more intelligent so that it allows using custom logging handlers. Now you just need to implement SimpleSAML\Logger\LogginghandlerInterface in a class, and set the 'logging.handler' option in the configuration file to a string with the full name of your class.

Move SimpleSAML_Metadata_MetaDataStorageHandlerMDX to SimpleSAML\Metadata\Sources\MDQ, and stop referring to it as MDX elsewhere.

Another bugfix: sometimes, very early during execution, a class with namespaces might not be autoloaded yet, and if we are asked to load the old class without namespaces, it will fail. Make it load the file corresponding to the class first, and see if it exists then. If not, try to see if it has been migrated to namespaces, and create the alias then.

Bugfix: don't try to log anything before creating a class alias, as the logger itself might be subject to an alias.

Add a temporary autoloader that allows loading old classes (SimpleSAML_Path_Something) that have already migrated to namespaces (SimpleSAML\Path\Something), while logging a warning. This commit requires to regenerate the composer autoloader with ./composer.phar dump-autoload.

Make the module autoloader to register class aliases for the classes that are migrated to namespaces, so that they are still accessible via the old name. This keeps everything working while migrating the classes.

Add a PSR-4 autoloader for modules. Now modules can declare their classes under the SimpleSAML\Module namespace.

This patch also starts using Composer for other dependencies
(i.e. php-openid and xmlseclibs).

Thanks to Boy Baukema for implementing this!

git-svn-id: https://simplesamlphp.googlecode.com/svn/trunk@3290 44740490-163a-0410-bde0-09ae8108e29a