add 2htdp/test port numbers to the list
raco setup: detect binary-only `setup/scribble`
scribblings/main: keep doc modules in binary mode

Even in binary mode, the "main" documents need to be re-rendered
when new packages are installed.
raco pkg: fix binary stripping of submodules
raco setup: clean up "library" installs that are directories
raco pkg create: adjust rules for for `{binary,source}-keep-files`

Allow `{binary,source}-keep-files` to override omission of an
enclosing directory. Also, adjust the default for binary mode to
keep "doc" and "info.rkt" within "scribblings" and not "tests".

With this change, starting with Minimal Racket and installing DrRacket
in binary mode gets you a working DrRacket with documentation. A
binary install is less than half the space of a non-binary install,
in part because the binary installation has fewer dependencies.