Only kick off project pref loading when the project changes

[dangoor]

This is a fix for #7250. What was happening is that there was a file tree refresh occurring and that was causing the PreferencesManager._setCurrentEditingFile in _loadProject to fire. The purpose of that call is to start the loading of project-level prefs, but in this case we weren't actually loading a new project and the result was that the preferences context for editing was being set incorrectly.

[peterflynn]

@dangoor Do we understand why setting the 'current file' back to the project root was resulting in incorrect JSLint options? The "jslint.options" in our project file isn't path specific, so it seems like any path in the project should yield the same options settings...

[dangoor]

@peterflynn Good question. It turns out that the project scope was being excluded when the project root was the same as the "current editing file". I just pushed a change that makes it so that project scope is also included in that case.

The first fix is still a valid improvement, because if there was a path-scoped preference it would improperly not be applied if _loadProject was called when a new project wasn't actually being loaded.

[peterflynn]

Makes sense -- fixes look good to me!

[dangoor]

@bchintx Peter's cool with this, but you're the reviewer of record. Want to take a look?

[bchintx]

Changes look good to me too. Merging...