redex: fix and clean up metafunction expansion

- defer disequation expansion so that generated code
  is linear w/r/t to the number of clauses
- fix variable renaming for disequations
Fix type of tanh.

Found using random testing.
raco pkg: fix conflict checking for a collection splice

Package updating also seems to have been broken by roughly
the same code (so maybe I ran the test suite incorrectly
before?).

Closes PR 13736
Add a few examples to syntax transformer section
A kindler, gentler death re: Robby
Fix cookie test re version
New Racket version 5.3.4.9.
share submodules of racket/base and scheme/base
for user code
remove dead code

The removed line was added due to a misreading of a failure
path as a slow path.

Thanks to Jon Zeppieri.
Move `explode-path' from `racket/path' to `racket/base'

The revised `explode-path' runs in time proportional to the
length of the path, instead of quadratic in the number of
path elements. The difference doesn't matter much in my
program, but I'm reluctant to leaving the implementation
as quadratic (which is forced by using `split-path').
render non-installaction-scoped package docs with an indirection

The indirection uses a "local-redirect.js" script to rewrite
the document links to local links within the browser. This mechanism
is a step towards distributing compiled packages that include
already-built documentation, where paths to other documentation
can be different than in the build environment.

If the links are not rewritten, they are queries to
"pkg-docs.racket-lang.org", with the idea tha such a server will exist
for reading all package documentation online. Also, a package's
documentation that refer to documentation for uninstalled packages,
in which case the corresponding links will not get rewritten and
will continue to point to the server.

Rendering the "local-redirect.js" script spends a lot of time just
converting among different path formats. Various library changes in
this commit are aimed at speed up those conversions, but the big
improvement came from a `path->url-string' that shortcuts conversion
os simple Unix paths.
raco pkg: "indices" -> "catalogs" in dependency message
avoid a constant folding that can use too much memory

Closes PR 13738
raco setup: fix subcollection traversal

Closes PR 13740
fix place-channel test
v5.3.4 installers info
raco exe: enable on-demand parsing of embedded bytecode

Creating a stand-alone executable could slow down a program,
because bytecode embedded in an executable was not treated
in the same way as bytecode loaded from files. The difference
was in on-demand parsing of bytecode --- and now it's enabled
for embedded bytecode, too.
fix `raco exe' test
Adding customization of command-char to web-server/template

This entails adding it to include/text and read-syntax-inside as well.
fixed (~r 0 #:notation 'exponential ....) bugs