Merge pull request #1975 from philfreo/master

Correcting upgrade guide for collection.fetch({add: true})
better to link to the method than try to re-describe it
Fixes #1977 -- add a test to ensure that default values work with merge (they do).
Fixes #1938 -- Splits up 'error' into two events: 'error' (for XHR) and 'invalid' (for client side validation) errors.
#1977 update test to fail
#1938 continued. Removing the options.error callback for client-side validation, adding model.validationError for convenient reference.
Merge branch 'master' of github.com:documentcloud/backbone
Really fix #1977 - models with default values merge properly
first draft of 'simple'
progress
... progress ...
removing a bit of 'silent'
... progress ...
right up to the edge ... nested sets are the next challenge
added test to show listenTo called on the same object
Add test for #1989
Fix #1987 - Be consistent when passing options to trigger callbacks
Fix #1978 - Correctly document `model.urlRoot` and `collection.url`
Merge pull request #1993 from caseywebdev/options

Fix #1987 - Be consistent when passing options to trigger callbacks
Merge pull request #1991 from gsamokovarov/model-change-test

Add test for #1989