Allow getLast{Result,Error} to enforce variables equality.
Allow getLast{Result,Error} to enforce variables equality.

I might prefer the default behavior to be reversed (variables must match
by default), but these are `public` methods of `ObservableQuery`, so we
should be careful to preserve the same behavior when `getLastResult` or
`getLastError` are called with no arguments.

apollographql/apollo-client,apollographql/apollo-client