function _setCurrentFile(newFilename) {
        var oldFilename = currentFilename;
        if (oldFilename === newFilename) {
            return;
        }
        currentFilename = newFilename;
        _toggleProjectScope();
        PreferencesImpl.manager.signalContextChanged(_buildContext(oldFilename, currentLanguageId),
                                                     _buildContext(newFilename, currentLanguageId));
    }
@private

This is used internally within Brackets for the EditorManager to signal
to the preferences what the currently edited file is.

@param {string} newFilename Full path to currently edited file