distro-build: split vbox control to separate module
raco pkg catalog-archive: build on `raco pkg catalog-copy`

... instead of `pkg-catalog-update-local`.
file/[un]zip: add UTC and time-rounding option

A `zip` archive normally holds timestamps in local time; a new option
records/interprets a UTC time instead. (Use the option both to zip and
unzip.) Also, add an option to round the 2-second resolution of time
to the past instead of the future (to avoid files with timestamps in
the future) when zipping.
pkg/lib: create and unpack ".zip" files with timestamps as UTC
distro-build: create ".zip" files with timestamps as UTC
raco setup: fix dependency checking for "racket" as a dependency