Please ignore the generated patches, left here for Martin’s benefit, and review the manually attached fix-5845.diff.

I have used read_init_file instead of hard-coding tab (it’s anyway the default for readline).

I may have repeated the same info in too much doc files, but I preferred to have more than one place where people could learn about the new behavior.  Advice welcomed.

If the basic approach looks good, especially if site still feels the right place for this, I will add tests.