fix chaperones and `prop:procedure` functions with keyword arguments

Commit 5bae9773aa broke `chaperone-procedure` and `impersonate-procedure`
so that it didn't always produce a chaperone or impersonator. Also,
the arity-error changeds intended for that commit were not complete,
because tests were accidentally commented out.

The main repair involves a new internal property that keeps track of an
accessor that is used to extract a procedure from a field in a structure
type that has `prop:procedure`.
updated stepper HISTORY.

Please merge to 6.0 release
oops 6.0 not 5.6, silly rabbit.

Please merge to 6.0 release
fix any-wrap/c for promises
Fix test cases for close?
make installers: fixes for `parallel` mode and timeouts

The `parallel` form in a site configuration was working only
with leaf machines; now, it should be fixed for `sequential`
nested under `parallel`.

Also, fix timeout handling and reporting of failures.
fix `chaperone-procedure` wth extra properies

Continues the saga of 5bae9773a, this time fixing chaperone
properties.
Test the error message instead of a predicate

This test was broken prior to commit 370c4bd but
didn't fail because the test harness didn't test for
the right error.
fix rendering of column by `srcloc->string`
at-exp reader: fix source locations in `read` error message

A change in `raise-reader-error` to use `srcloc->string` caused
tests to fail because `srcloc->string` doesn't show location
information if the source is #f.
Scribble->Markdown titles are now rendered correctly. Sections have been shifted by one level (which also looks better on Github).

Markdown: fix defmodule to avoid printing the package in the example

fix markdown example file to make test pass
enable scribble tests for DrDr
history for 2htdp teachpacks
apply signature in productbuild, not pkgbuild

Merge to release branch.
remove extraneous CRLF after message-body

RFC2616 section 4.1 (http://www.ietf.org/rfc/rfc2616.txt):
"... an HTTP/1.1 client MUST NOT preface or follow a request
with an extra CRLF."
scribble: fix a test to make it independent of the enclosing package
dynamic-require: fast path for re-exported variables

When `dynamic-require` is used to access an export that isn't a
variable defined in the same module, `dynamic-require` falls
back to `eval` in a fresh namespace, which can be expensive.
The new fast path handles the case that a variable is re-exported.

The new fast path is relevant to deserialization, which now
uses a submodule that re-exports from an enclosing module.
increase timeout of `raco exe` test suite
fix closure type tracking for a procedure with only an unused rest arg

Closes PR 14259
compiler/zo-structs: fix docs to note 'fixnum and 'flonum types