Adding proxy methods in lazy_array.rb doesn't account for assignment methods

LazyArray dynamically defines all the Array and Enumerable instance methods on itself. However, it does not account for the difference in assignment methods. While you can define a method as follows in Ruby, you can't call it directly (you can #send to it though):

$ irb
>> def foo=(*args, &block)
>> p args, block
>> end
=> nil
>> args = [:a, :b, :c]
=> [:a, :b, :c]
>> block = lambda { 1 }
=> #<Proc:0x005d4f30@(irb):5>
>> foo = *args, &block
SyntaxError: compile error
(irb):6: syntax error, unexpected ',', expecting $end
foo = *args, &block
            ^
        from (irb):6

This causes an exception in Rubinius where we have same addition accessors on Array:

http://pastie.org/399089