Accurately report cache sizes before and after purge.

This fixes a merge resolution mishap that occurred in 178be5393fcfaf860c72ba2b9f26acc05b621375.

Also property state units, it's bytes (B) not bits (b), and report kiB when claiming to do so, not MiB.
Merge pull request #2740 from thobe/2.0-cache-purge-statistics

Accurately report cache sizes before and after purge.