futures: fix a problem in cgc mode
futures: fix bug related to tail calls
Fixed some transforms, stubbed out docs and examples for the same
adjust repl-test and the module language test for the new error message format
adjust global-port-print-handler's documented contract to match
what it does (and what the text says)
fixed a bug in the ordering of how printing parameters are set up

There was an exception raised and then handled internally when the
slideshow/pict-convert library was loaded; DrRacket loaded this
library during the dynamic-extent of a handler it installed into
the global-port-print-handler, which causes a (non-tail) infinite
loop.
Adjust how the drracket repl iterates over expressions to make it more
like textual-read-eval-print-loop

There is still a difference, however, because drracket's REPL has a
notion of multiple expressions that are submitted simultaneously that
textual-read-eval-print-loop doesn't. For example, if you type this at
the prompt:

  (car) (+ 1 2)

then textual-read-eval-print-loop will print out the error and then 3,
but drracket will print only the error (ditto if (car) were replaced
by a continuation abort).

This difference is, IMO, a good thing, since it lets you use a single
interaction to do multiple things, but stops as soon as there is an
error. (It is also how drracket has behaved for a long time.)

closes PR 12790
racket/gui: fix `canvas%' implementation `on-paint'

Broken in the conversion from `class100'.
Add support for multiple provides of the same identifier in TR.

Closes PR 12807.
further correction to tests/gracket/blits prop

The test isn't automatic, so don't run it in DrDr.
configure: use installed `libtool' by default

But libtool is used only for `--enabled-shared' builds.
ffi/unsafe: fix arithmetic overflow and representation

Thanks to Tobias Hammer for the report and initial repairs.
adjust the timeouts to two drracket tests and add a little syncronization help in a third
adjust redex error message tests to match singular/plural fixes in
the error raising code, except in one place where I think the
error raising code was correct to have the plural form, so I changed
it back instead of changing the Redex test suite to match
Attach struct info to constructor for polymorphic TR structs.

Closes PR 12806
add PLTJUSTSAVEFAILURES support; makes it easier to build a good
set of bitmaps on others' machines (no clicking required)
adjusted the module-language, pretty-big and r5rs parts of
the drracket language test for the new error messages
Adjust datalog to cooperate with check syntax a little bit more.

Specifically:
 - make predicate symbols and variables be original (and,
   in the former case, have srclocs)
 - remove the originality in the quoted syntax constants
   that the expansion introduces

I think there is probably something better that should be done
with those introduced syntax constants, possibly relacing
them with #f, or possibly replacing them with source location
lists, but I'm not sure how they are used, so I've just left
them in there.

(Also, very minor Rackety in check syntax)
fix easter egg test suite for the new error messages
Redefine Boolean as (U #t #f).

Closes PR 12815.