Default field values should be added to responses as clones, rather than by reference

[Radagaisus]

This solves an issue where modifying responses would "pollute" default values for other queries.

• Now using the node-clone package, version 1.0.2
• Fixed the issue: default values will be cloned before being added to the response
• Prettified the code around the cloning of the default value a bit
• Added a validation test

    # This test validates that default field values are cloned and passed by-value
    # to the response, rather than by-reference. If the end-user tries to modify
    # a response that contains by-reference default fields, this can "pollute"
    # default values for other queries. The scenario we test here:
    # 
    #1. Every reader has a set of books that defaults to an empty array.
    #2. We retrieve the first reader's (empty) list of books
    #3. We update that list with a new book that that reader has read
    #4. We retrieve the second reader's (empty) list of books.
    # 
    # When default values are passed by-reference, this would've caused the second
    # reader's list of books to be "polluted" with the first readers book. Cloning
    # the default value takes care of this.
    # 
    it 'Default field values are returned in the response as clones', (done) -> 
        # Define a new Reader model, that holds a set of books they've read, that
        # defaults to an empty array. Arrays are by-reference in JavaScript.
        class Reader extends Orpheus
            constructor: ->
                @set 'books', default: []
        # Create the reader API
        reader = Reader.create()
        # Retrieve the first reader's books. The first reader has no books yet,
        # so this will return the default value - an empty array.
        reader('first').books.members().exec (err, res) ->
            # Update the reader's books with a new book they've read.
            res.books.push('The Great Hunt')
            # Update the books set for the first reader in the database. This step
            # is not really needed for the test, but it helps illustrate a real
            # world scenario for this issue.
            reader('first').books.add(res.books).exec (err, res) ->
                # Retrieve the books of the second reader. The second reader has no
                # books yet, so we expect the list to be empty. The bug we test here
                # would have caused the empty default array to be "polluted" with the
                # first reader's books.
                reader('second').books.members().exec (err, res) ->
                    # Check that the books list is empty
                    expect(res.books.length).toEqual 0
                    # We're done.
                    done()