[1.7.x] Fixed typo in docs/topics/db/managers.txt

Backport of 9e8658db51 from master
[1.7.x] Fixed #17638 -- Added crosslinks between topic and reference guides.

Thanks oinopion for the suggestion and jarus for the initial patch.

Backport of 054bdfeff1 from master
[1.7.x] Required numpy < 1.9 for tests; refs #23489.