generalize `{impersonator,chaperone}-of?` on immutable hash tables
raco setup: repair clean-up of PLaneT info-domain cache

Unintentional shadowing caused the info-domain clean-up code to reject
all PLaneT path registrations. As a result, installing a PLaneT
package removes all info-domain mappings (used to find documentation,
`raco` commands, etc.) for other PLaneT packages. Running `raco setup`
repairs the problem, because it re-adds all entries after
(incorrectly) clearing them out.