Fix fallout from the emancipation of dump(8) workers

[cperciva]

Summary

The change from "slave" processes to "minion" processes to "worker" processes left some less-than-coherent names:

1. "enslave" turned into the ungrammatical "enworker".
2. "slp" (SLave Pointer) turned into "mlp" (Minion [L] Pointer?).

Convert "enworker" to "create_workers" (the function in question forks off 3 worker processes), and replace "mlp" with "wp" (Worker Pointer) and "tmlp" with "twp" (Temporary Worker Pointer).

[danfe]

Thanks for taking care of this Colin. The diff looks fine at a quick glance.

[cem]

Diff looks good to me, thanks. I would suggest not using "emancipation" in the commit subject.

[imp]

Thanks Colin!

[mckusick]

Thanks for this cleanup. I found the previous transformation grating for the reasons that you listed.