fix redex docs

closes PR 14450
racket/class: fix empty `define-values`

Closes PR 14451
More TR class adjustments for expansion changes
some work on random generation from contracts
update Redex to cooperate with the new undefined semantics
make the teaching languages cooperate with the new undefined semantics
add missing release notes

Please include in 6.0.1
Sync German string constants with latest.
add some debugging information into the module language test suite

specifically, when tests fail and there is an error icon in the REPL,
then go find the stack associated with it and print it out
fix a non-buggy set!-before-initialization in syntax-browser

What appears to be happening is that the fields path and next-push
are state variables on this class that are initialized and then used
only during the dynamic-extent of syntax-object->datum/record-paths
and of the pretty-printing code.

So, before the check was in place, they were initialized and used
before the 'path' field was initialized, but by the time the path
field was initialized, the value was junk (not going to be used again)
but it still raised an error
Fix `typecheck-fail` in TR

Closes PR 14449
Clarify Datalog/Racket interaction re Matthias
Update HISTORY.txt for stepper

Please merge to 6.0.1 release
Replaced JPG file with PNG, so future renderer changes don't break test
cases.  Please merge to release branch.
Merge branch 'master' of pltgit:plt
Improve source location tracking for TR classes

Closes PR 14400
Adjust TR class error messages

Use the new error message format for most cases.
Convert some internal errors to use int-err.
Improve code for checking init args for TR classes
fix drracket-specific keybindings to work with alt-as-meta preference
fix references to subdirectories of a rendered manual

For example, fix the resolution of a link to a binding in the R5RS
or R6RS spec.