Fix classes that extend modules where contracts were included

[waterlink]

Fixes #176

Our current routine while including or extending Contracts is to define Contract(*args) method for current class and make it just delegate to self.class.Contract. But in case of:

m = Module.new do
  include Contracts::Core
end

Class.new do
  include Contracts::Core
  extend m

  Contract String => nil
  def foo(x)
  end
end

it doesn't work, since there is no self.class.Contract at this point of time. But, there is just Contract already in super class, and we may just call it. That is what this PR does: verifies if there is a Contract method in super class and calls it instead of delegating to self.class.Contract.

/cc @PikachuEXE @egonSchiele

[waterlink]

@PikachuEXE Can you verify that this branch https://github.com/waterlink/contracts.ruby/tree/fix/176/classes_with_extended_modules_with_contracts fixes the problem for you?

[waterlink]

Hmm, this fix doesn't work with ruby 1.9.2 only.

[waterlink]

Ok, now it works for every ruby :)

[PikachuEXE]

@waterlink
Your branch works for the test script and my project :)
Which is #198 ?

[PikachuEXE]

Wait I am in #198 now

[PikachuEXE]

I got another question
Should I include Contracts::Core or Contracts? (for latest versions)
I don't want to use the deprecated one :)

[alex-fedorov]

Contracts::Core is better in terms of not having all our helper classes in your namespace. But it means you don't have builtin contracts either.

Before we fully forbid usage of include Contracts, we will add include Contracts::Builtin. This way, you will be able to do:

include Contracts::Core
include Contracts::Builtin

And you will get original functionality that you have had before with include Contracts but without our helper classes in your namespace.

[egonSchiele]

lgtm

[PikachuEXE]

Hope to see Contracts::Builtin soon :)

[alex-fedorov]

@PikachuEXE this is very simple change. Maybe you are up for making a PR?

[PikachuEXE]

Contracts::Builtin or Contracts::BuiltinContracts?

[alex-fedorov]

Contracts::BuiltinContracts sounds like a repetition (you already have Contracts:: at beginning), so Contracts::Builtin it is.