Pre-release #1 of Sinon 2

• Fix #875 Proper support UTF8 payloads
• CommonJS-ified some of the things
• updated readyStateChange to align to the w3c spec (somewhat)
• added some additional progress event verification
• added a test to ensure load is not fired before abort
• added test to ensure event ordering
• allow progress events with loaded/total values of 0
• Fix #867: Walk properties only once
• Removed unnecessary module wrappers and double test run in NodeJS.
• null-check the object passed to sinon.stub
• implemented stub#resetHistory method - fixes #863
• Fix #851: Do not attempt to re-stub constructors
• Fix #847: Ensure walk invokes accessors directly on target
• stub.reset also resets behavior