Re-integrate community-reviewed and -merged changes into mainline

This pull request accumulates community-reviewed (by at least Brian Hawley, Ladislav Mecir, and myself), tested, and merged changes.

By merging this single pull request, all changes already merged into the "community" repository (rebolsource/r3) will be merged into the "mainline" repository (rebol/r3). The separate, earlier pull requests related to the merged changes will be automatically marked as merged and closed.