Fix set-symmetric-difference docs.
Fix bug with equal? on small bit-vectors.
Fix init order of choice%'s type
Synch German string constants with latest.
meta/pkg-build: fix potential problem with cycle detection

Also, correct typos and out-of-date information in comments that
serve as documentation.
meta/pkg-build: add support for "minimal" vs. full VMs

Try building on a minimal VM, first, and then fall back to a more
general VM is that fails. For example, a minimal VM might not include
a C compiler, which can help clarify that a package will work in some
environments and not in others.
meta/pkg-build: run `raco test --drdr` for each package
meta/pkg-build: always set the VM clock

Consistent installation depends on a global clock that always
moves forward, so make sure VMs stay in sync.
meta/pkg-build: keep test-success log (same as test-failure)
simplify and extend the find-string method in text%

This implementation runs about 10% faster than the old when searching
for "λ" in (collection-file-path "unit.rkt" "drracket" "private"). It
is copied directly from the search search algorithm from Wikipedia
called Knuth-Morris-Pratt, but with a fancier version of get-char that
cooperates with text%'s snip interface for more efficient linear
scans of characters.

It also generalizes the previous one by supporting searching into
embedded text% objects inside editor-snip% objects

related to PR 14688
related to PR 14687
fix incorrect contact; closes PR 14798

please include in the 6.1.1 release
Use the scale when rendering svg

Thanks to Antonio Menezes Leitao for the change
meta/pkg-build: add an "about" page

Explain `raco test`, the `PLT_PKG_BUILD_SERVICE` environment variable,
and the "x86_64-linux-natipkg" platform.
meta/pkg-build: record start and end time for tests
fd write: accomodate non-partial writes to a non-full descriptor

If a write to a non-blocking descriptor fails, then try again
with fewer bytes, since nothing in the spec write() seems to
promise writing partial amounts. In particular, writing to
a FIFO no Mac OS X might fail even if there are a few bytes of
space; as it happens, the select() function seems to compensate
and claim that such a FIFO is full, but kqeueue() doesn't.
fd read and write: avoid redundant O_NONBLOCK flag setting
work around a kqueue bug(?) on Mac OS X

There seems to be a problem in kqueue() on Mac OS X for watching for
FIFO write availability, where adding a read event for the same FIFO
(at a different file descritor) can disable the write event.

Merge to v6.1.1
meta/pkg-build: edit the "about" page
make `read-line` interruptable on a primitive port

Closes PR 14800

Merge to v6.1.1
fix a contract example in the documentation

closes PR 14798 (the previous commit, 86017992ab, that
claimed to fix this PR is unrelated; sorry for that)

Please include in 6.1.1