Make users of check-below call it with same kind arguments.
Make check-below only accept arguments of the same kind.
Raise a better message for ctc generation in TR

This provides a better explanation of contract generation
failures for module-provided bindings.
Revise Scribble docs for the new package system

Replaced mentions of PLaneT with the new package system
in sec 4.1 of the Scribble docs.
Support rest args for TR class methods
Fix class typechecking for Name types

Fixed check-class-unit and get-field for the addition
of recursive Name types.
Adjust error messages for send typechecking
Make check-below-tests check more things and give more debug info.
Initial version of filter tests.
Fix implied-atomic to work on -top and -bot.
avoid unnecessary embedding of build path in generated doc support
meta/new-web: adjust download-site list
Fix type->contract for recursive Name types

Certain mutually recursive Name types would generate
contracts that infinite loop when triggered.
Change "Class and units" to "Unsupported features"

Also remove classes since they are supported now.

Closes PR 14398
meta/pkg-push: fix for "racket" package
scribble docs: tweak language related to collections and packages
document details of collection and package installation

This information is about internal implementation details, more or
less.  Some details can leak out, such as when files get mangled or
browser cookies get stuck. Mostly, though, the intent is to document
how various of pieces fit together to make builds and distributions
work.
scribble/manual docs: corrections on `#:link-target?` and `#:indirect`
setup/dirs: change default doc indirection to a useful URL
fix handling of code compiled to ignore

When the compiler sees `(if #f A B)`, it compiles A in a throwaway
mode, but the throwaway mode need to produce a slightly more plausible
result than it was so that further throwaway transformation is not
confused.