fix sandbox test to avoid influence from other tests
add `make-environment-variables'

Swap order of argument for `environment-variables-get'
and `environment-variables-set!', so that the environment
variables come first --- which follows the usual order.
This change means that the parameter isn't used to get
the default environment variables, but that seems ok; the
convenient interface is `getenv' and `putenv'.

On Windows, case-normalized environment variable names.

Also, change the implementation to use an immutable hash
internally.
fix hole in validator

The validator was not as smart as the compiler in determining
that a `let' expression could be relied on to produce a
constant-shaped function (without side effect or error) in the case
that a right-hand side expression is a call to a known structure
constructor or predicate.

Closes PR 13679

Merge to v5.3.4
add a consistency check on the final environment

Specifically, check that fully instantiated terms
with cstrs on them satisfy those cstrs.
sconfig adjustment to accomodate PPA build

The build process expects the definition of
SCHEME_PLATFORM_LIBRARY_SUBPATH to make sense as a shell
expression, or something like that.
performance tweaks for `for/{fx,fl,extfl}vector'

Also, provide a better error message when the body produces a
non-{fix,flo,extflo}num.
make opt/c use a more comprehensive list of known-to-be-good
predicate contracts

also make it just evaporate when the contract is unknown
(instead of leaving a wrapper behind around the contract)
Make configure install the docs in the standard place.

Closes #315 (on github)
New Racket version 5.3.4.3.
GC tweaks

In a minor collection, old-generation pages can be ignored for
the fixup pass. Also, the "moved" bit implies the "marked" bit.

Also, move the mark bits to low and the hash bits to high,
which leads to slightly better generated code for the GC.
fix the name of `environment-variables-ref'

Also, fix use of unsetenv() to work with platforms where it returns
void.
code tweaks
Fixing PR13683
Adding link
Changing default max-waiting to 511 re Apache
Adding max-waiting to serve/servlet, re dyoo
Normalize max-waiting contracts
pkg docs: add a tag for the "how to develop" section

Merge to v5.3.4
move `handin-client' and `handin-server' to `handin' package
raco setup: remove any extra documentation dirs in installation

After uninstalling a package in installation scope, its documentation
should be removed. A new `raco setup' step takes care of that.

Merge to v5.3.4