Description:
------------
Using multiple traits that depend on the same requirement using an abstract method fails with a fatal error.
I tried using trait composition in order to move the requirement into a common trait, but this does not work either.



Test script:
---------------
trait DoubleAmount {
    public function doubleAmount() {
        return $this->getAmount() * 2;
    }
    public abstract function getAmount();
}
trait TripleAmount {
    public function tripleAmount() {
        return $this->getAmount() * 3;
    }
    public abstract function getAmount();
}
class model {
    use DoubleAmount, TripleAmount;

    public function getAmount() {
        return 23;
    }
}

Actual result:
--------------
PHP Fatal error:  Can't inherit abstract function TripleAmount::getAmount() (previously declared abstract in DoubleAmount) in /home/maus/projects/traitstest/trait_abstract.php on line 30