Description:
------------
At the moment it is not possible to implement dependency managers that can handle different versions of the same package. If the callee (file location) would be provided as second parameter for autoload callbacks a autoloading implementation could determine the correct version to load.

Some real world example:

You start a new composer based project and require some third party package.
That package requires another package, for example some api.

So long all is good

Now you require one more package, that requires the same package but in another version => not possible.

A fix would be downwards compatible because the additional parameter would simply be ignored by current implementations.

Test script:
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// something like this 
spl_autoload_register(function($className, $originPath){
  get_real_autoloader($originPath)->load($className);
});