Log Message:
tex-memoir{,-doc}: update to 3.7.19

- changed version numbering to v3.7.<num> (no plans to switch to 3.8
  anytime soon)
- changed several \theH... definitions to \def to work better with
  coming hyperref/tagging changes
- similar for \toclevel at ... macros
- only declare \stockwidth and \stockheight if the kernel hadn't done
  so already