add an extra verification step to expectStreamEvents. Several failures found.
fix verifySwitching2: the unsub var wasn't correctly updated
fix verifySwitching2 again
skip verifySwitching2 for certain "unstable" streams
refactor
Merge branch 'verifySwitching2'

- Streams are tested with verifySwitching2 tester too
- Not all streams are stable under verifySwitching2 and this tester is skipped for them
- Generally, all flatMap-based streams are unstable because flatMap discards child streams on unsubscribe.