language cleanups in code and docs

Hi, We've removed the use of "slave" from most of the repo (one use remained, included here), but we didn't do the same for master. In the attached series I replaced most of the uses. 0001: tap tests: s/master/primary/ Pretty clear cut imo. 0002: code: s/master/primary/ This also includes a few minor other changes (s/in master/on the primary/, a few 'the's added). Perhaps it'd be better to do thos

[KoshianX]

なかなかにひどいことになってるなあ……。postmaster も名前変わんのかいな。ほんとにやるのこれ？