racket/gui Win32: fix use-before-definition problem for `choice%`

Closes PR 14475
Change test to use exact flonums instead of 0.1
I maintain planet
generalize the random contract generation so that it can exercise
a function to get more interesting values and then use those values
to guarantee it can generate things it couldn't before

For example, it can now generate a function with this contract:

  (-> (-> is-eleven?) is-eleven?)

without knowing what the is-eleven? predicate does -- instead it can
figure out to call the argument thunk and then pipe that result around
Remove code that handles #<undefined> in TR

TR no longer needs to handle #<undefined> because the value
no longer leaks out from uninitialized variables. However, uses
of uninitialized variables are not caught by TR (they are treated
like errors from the `error` function).
need CAS only for futures or places
configure: for BSDs, enable pthreads by default, but don't force enabled
fix wrong size for memset

Probably the assignments cover the structure, anyway.
linux: close "/proc/self/maps" after finding the stack base
raco setup: fix info-domain cleanup of unlinked planet packages
raco pkg: fix documentation indexing for user-scoped re-link

If a package installed as a link in user scope, then removed, then
linked again, the documentation index database was not updated
correctly. As a result, the user-specific documentation page was
either not updated or had a broken link for the document.
raco exe: attempt to fix problem with room made for runtime-paths table
fix performance bug in `equal?` on vectors
add some extra test cases on `equal?` and chaperones

The compiler defeated my original attempt to check arguments in
both orders, but now I see the obvious way to (probably) check
both orders.
xrepl: fix tests
fix `sync` on inaccessible place channel

Commit 5ea4c2ab68 broke GCing of a thread that is blocked
via `sync` (as opposed to `place-channel-get`) on a place
channel whose write end is inaccessible.
fix test
Update require/typed in no-check mode for keywords

Closes PR 14463
Fix require/typed in no-check mode for structs

The constructor name was handled incorrectly for TR's current
defaults. Also support the extra keyword arguments.
Refactor TR's no-check-helper module