Report deprecation when calling methods of a deprecated trait

[devfrey]

Closes #128

When a trait is marked @deprecated, calls to its methods are now reported as deprecation errors — for both instance and static calls.

Example:

/** @deprecated use something else */
trait MyTrait {
    public function doFoo() {}
}

class X {
    use MyTrait;
}

$x = new X();
$x->doFoo(); // Call to method doFoo() of deprecated trait MyTrait: use something else