Updated Backbone.Validations to work with Backbone 0.9.10

[spmason]

Backbone 0.9.10 has some fairly big changes to validation, though the changes to Backbone.Validations are confined to the newPerformValidation function

I've just made it re-use the default Backbone._validate function instead of re-implementing it, to save some hassle. Some extra work is required to raise invalid:prop events, you wouldn't have to override _validate at all if it didn't have to raise these..

For reference, the new behaviour is as follows:

• invalid events are now raised for validation errors as error is now reserved for xhr errors (this is badly documented but the correct behaviour: Failed validation does not trigger error callback jashkenas/backbone#2153)
• To get validation to fire on set, call with {validate: true} (I had to update the unit tests)
• The error callback is not called on validation errors, you can inspect the model.validationError property instead, immediately after calling save

[nealstewart]

Looks great!

Thanks for updating the tests. You rule.