Invalidate constant cache if included module has constants

JRuby currently does not invalidate the global constant cache serial number if an included module has constants.

This means that cached constant lookups could return incorrect results.

Here's a little test script demonstrating the incorrect behaviour:

```ruby
A = 1

class Foo
  def self.go
    A
  end
end

module M
  A = 2
end

puts Foo.go # prints 1

Foo.send(:include, M)

puts Foo.go # should print 2, prints 1
```