Better error messages for class/object contracts
describe some additional errors in docs for require
Small changes/fixes to rackunit.

* Add optional message for fail-check.
* Correctly shorten column name.
Move benchmarks to `racket-benchmark` package.
Move doc completeness check to where it belongs.

The odd file name is to avoid package system clashes.
Fix props for benchmark move
add list? to ISL+, Racket; Closes PR14103
fixed docs for atan
moved run to xrun file
Make Typed Racket build with contracts again
Adjust contract on make-pred-ty

Allow old-style and new-style filter path objects.
add pkg desc for "racket-benchmarks"
fix scribble interaction error msg

fix error msg when scribble interaction #:eval
does not have sandbox-error-output set to 'string
Synch German string constants with latest.
make installer: option to set address & port where server listened

Client SSH connections now create remote port forwarding port back
to the server, so that making the server listen only on "localhost"
provides an easy improvement for security (except that remote port
forwarding seems not to work with freeSSHd on Windows).
make installer: make Windows work with bash-serving sshd

Makes a Windows build client work with Cygwin's opensshd.
make installers: make the server listen only to "localhost" by default

This makes the build more secure, but it's a backward-incompatible change.
To adapt old site-configuration scripts, the simplest option is to set
`#:server' to "localhost" everywhere and rely on SSH tunneling to let
a client reach a server (though, unfortunately, that option doesn't
seem to work if a Windows machine uses freeSSHd). Another possibility
is to se `#:server-hosts' to the empty list.
Mac OS X: make updated frameowrk paths a multiple of 8

Needed for code-signing (on 64-bit builds, at least)
make installer: add Mac OS X code-signing support
make snapshot-site: add "current" links for installers