fix `exn:fail:filesystem:missing-module-path'
Add optional message flags argument to imap-append.

Previously this was hard-coded to use the \Seen flag. Now that's the
default value when the argument is not supplied.
ffi/unsafe: fix memory-management problem in recent change

Fixes a problem with bba223a9fe.
fix contract
modernize a few contracts in drracket
add a few more contracts to those that opt/c recognizes and
fix a few bugs in existing ones

also, adjust opt/c so that it logs failures to optimize on its own logger
make contract structs print a little bit more nicely.
New Racket version 5.3.4.5.
fix a JIT bug related to inlined structure constructors

Merge to v5.3.4
file/gunzip: fix problem with lookahead handling

If less than the lookahead bytes have been pulled in, then the
old code would attempt to read a negative number of bytes.
raco setup: put launchers for user collections in user space

Also, remove executables (in full setup or "tidy" mode) when the
corresponding collections are removed.

As a result of these changes, `raco pkg' puts launchers from user-scoped
packages in user space and cleans up launchers from removed packages.

There's no attempt to include "launchers.rktd" in a distribution.
That should be ok: having an entry in "launchers.rktd" just
makes a launcher a candidate for removal. Including "launchers.rktd"
would be a hassle for many reasons, including that the initial set
of launchers is platform-specific.
fixes for Windows related to missing-module exceptions
update for 5.3.4
fix jump-to-defining-file when a stacktrace window is open
raco dist: update ELF section when adjusting data size

Merge to v5.3.4
Use information of application site, to reduce possible arities.

Closes PR12905.
Small TR fixes.
Fix up lazy-requires and dynamic-requires in TR.
Don't let map introduce type variables.

Closes PR 13581.
Fix expected type when typechecking map