Add channel chaperones

These chaperones only protect the "put" end of the
channel and use evt chaperones to protect the "get"
end.
Update HISTORY
Use the new #:keep-going? option for TR random testing.
Allowing any user to add tag again
Fixing PR14136
doc correction: interior pointers cannot be odd-valued

More precisely odd-valued references do not prevent GC
of an enclosing object that is allocated in "interior" mode.
db/sqlite3: fix memory-management problem

The sqlite3_prepare[_v2]() function takes a byte-string pointer
for a query and returns a pointer into the byte string. That
pointer can be odd-valued, in which case the GC doesn't treat
the pointer as a reference to the byte string (even when the
string is allocated with 'atomic-interior), so arrange for the
original pointer to be retained.
Synch German string constants with latest.
typo

(sure would be nice if this were a syntax error)
adjust tc-setup to have a smaller template
IN PROGRESS: enable opt/c on provide/contract and define/contract (via with-contract)
IN PROGRESS: working on rect support for error messages for 2d cond
Log types of expressions and fully expanded syntax (before typechecking)
IN PROGRESS: working on changing the protocol between the
expanding place and the drracket place to support sending information
during the expansion process, not just at the end
Sorry all; stupid mistake

This reverts commit 90fc899b368bbbd16d284d03dcef53039fffbfca.
This reverts commit 780fb37c0dab0bdab8b91a083660ae88021435e8.
This reverts commit 9e54b2bc1b8c0ca8a3d84b86a438153e8e1ff2e7.
This reverts commit 43a584f7105ba3a0d7830879003a8c5241258969.
unbreak TR (more of my stupidity)
Add concurrency chapter to the Guide
fix docs for `wrap-evt`

The prohibition against `handle-evt` results has been dropped.
guide: small edits to concurrency chapter

Also, split sections on futures and places into a "parallelism" chapter.
drop unneeded #include

The "sys/param.h" header was used to check the OpenBSD version.
It's not needed, anymore.