Set the value and signal so that, someone waiting for value can retrieve it

Property definitions

actors $ Future :: set_value
	# Set the value and signal so that, someone waiting for `value` can retrieve it
	fun set_value(value: E) do
		mutex.lock
		is_done = true
		self.value = value
		var cond = self.cond
		if cond != null then cond.signal
		mutex.unlock
	end
lib/actors/actors.nit:182,2--190,4