add shouldResubscribe option

[gilesbradshaw]

A should resubscribe option makes subscription queries optionally resubscribe when the props change..

I use it like this:

const NODE_SUBSCRIPTION_QUERY = gql`
  subscription  - blah blah ....

const NODE_QUERY = gql`
  query  - blah blah ....

const _Node = (props) => <Blah />

const options = {
  shouldResubscribe: (props, nextProps) => {
    // if the id property changes then we need to resubscribe..
    return nextProps.id !== props.id
  }
}
const Node = compose(
  graphql(NODE_SUBSCRIPTION_QUERY, options),
  graphql(NODE_QUERY)
)(_Node)

[apollo-cla]

@gilesbradshaw: Thank you for submitting a pull request! Before we can merge it, you'll need to sign the Meteor Contributor Agreement here: https://contribute.meteor.com/

[jbaxleyiii]

@gilesbradshaw nice! can you add this to the docs site as well?

[gilesbradshaw]

sure! apollostack/react-docs#138