Add a Project#dirty? method

[alloy]

This should return whether or not any changes have been made to the project since it was loaded from disk.

It would remove the need for most/all of these changes CocoaPods/CocoaPods#2606.

/cc @segiddins

[neonichu]

I'd say once #199 is implemented, we can just save whenever we want, just like Xcode does :)

[alloy]

@neonichu Good point. I guess I’m just a little conservative and wouldn’t want the project to unnecessarily get saved in situations where we fallback to normal CFPropertyList handling (when Xcode can’t be located or the frameworks can’t be loaded).

[kylef]

@neonichu We shouldn't save all the time, only when changed. Stop harming my SSD write cycles you!

[neonichu]

@kylef I hope you never use Xcode to work with your project, then :)

[alloy]

work

LOL

[kylef]

When this work is done, be sure to refactor CocoaPods to make use of it: CocoaPods/CocoaPods@81f85e0#diff-7dd6f660fb1a2603c42ffb5de8c97297R30