Walkthrough of pending TODO 2.2 remarks

that were left there while doing major refactorings for 2.2. All such
TODOs have been either:
- implemented
- removed since no longer valid
- converted into a "regular" TODO since it's not a 2.2 specific concern
Merge pull request #3194 from tinwelint/todocleanup

[2.2] Walkthrough of pending TODO 2.2 remarks