Merge #7992: Extend #7956 with one more test.
269a440 Add test for dbwrapper iterators with same-prefix keys. (Matt Corallo)
6030625 test: Add more thorough test for dbwrapper iterators (Wladimir J. van der Laan)
84c13e7 chain: Add assertion in case of missing records in index db (Wladimir J. van der Laan)