NOBUG: Allow T_CLONE to be used as function.

While it's really not nice, we have tons of (historic) uses of clone() as a function, so we should not be producing any error for them.

This subclasses the original PHPCompatibility sniff in charge of detecting such incorrect function uses and gets rid of the clone() verification.

Backed with tests to verify that other checks continue working and our require/include/clone duality is allowed.

Ciao :-)