Re-add missing members if only some were re-added after failed excludeMembers

[Powersource]

Part of https://github.com/ssbc/ssb-tribes2/issues/123

• [x] Test. Use this trick https://github.com/ssbc/ssb-tribes2/issues/107
• [x] document timeoutScale

[mixmix]

Seems like failing test is on me :

Happily alice and bob agree on the preferred epoch, but might both be off-spec D:

[Powersource]

wait where did you get the failing test?