net/http-client: fix `http-conn-live?` result

Merge to v6.0
Synch German string constants with latest.
fix a synchronization problem in the GC for places

When a GC is needed for the shared space, a GC is triggered
in all places, and the places wait until each other place
has completed. However, the places also need to wait until
all other places are ready to *start* a GC; otherwise, a
place may be modifying a shared record while some other place
traverses it for a GC.

Closes PR 14229

Merge to v6.0
Add more documentation for `Procedure` type

Please merge to v6.0
Describe how to make packages compatible with 5.3.5 and 5.3.6.

As requested by Sam Tobin-Hochstadt on the mailing list today.

Merge to v6.0
Remove extraneous compile of non existent file.

Merge to v6.0
* Parameterized comment-reader over 'unsyntax, for use with RACKETBLOCK
  pkgs/scribble-pkgs/scribble-lib/scribble/comment-reader.rkt
* Updated manual to explain #:escape-id parameter to comment-reader
  pkgs/scribble-pkgs/scribble-doc/scribblings/scribble/manual.scrbl
* Changed parameter name to #:escape-id.
  pkgs/scribble-pkgs/scribble-lib/scribble/comment-reader.rkt
* Changed parsing for #:escape-id to use a peeking-input-port.
  pkgs/scribble-pkgs/scribble-lib/scribble/comment-reader.rkt
scribble/comment-reader doc tweaks
Add n-ary cartesian-product to unstable/list.
Fixed bug 14177

bezout-binary did not handle negative numbers correctly.
Fixed a few errors caught by Pierpaolo.
Make type of expt more precise on floats.

Closes PR14228.
Fix types for `remove` and friends.

A few of these had unnecessary uses of type variables.
The type for `remove*` was unsound.

Please merge to v6.0
Remove unused type variable.
Document version exceptions.
fix bug in number rendering
tweak the spacing in the bernoulli sequence
fix stacks when in test coverage mode

(most of the commit is a rather involved test case....)