Correctly assign a left and a right value

Boxing and unboxing is performed if required

Property definitions

nitc $ AbstractCompilerVisitor :: assign
	# Correctly assign a left and a right value
	# Boxing and unboxing is performed if required
	fun assign(left, right: RuntimeVariable)
	do
		right = self.autobox(right, left.mtype)
		self.add("{left} = {right};")
	end
src/compiler/abstract_compiler.nit:1659,2--1665,4