The rule against difficulty adjustments changing by more than a factor of 4 can
be helpful for anti-DoS measures in contexts where we lack a full headers
chain, so expose this functionality separately and in the narrow case where we
only know the height, new value, and old value.
Includes fuzz test by Martin Zumsande.
Blindly chose a cap of 10000 iterations for every loop, except for
the two in script_ops.cpp and scriptnum_ops.cpp which appeared to
(sometimes) be deserializing individual bytes; capped those to one
million to ensure that sometimes we try working with massive scripts.
There was also one fuzzer-controlled loop in timedata.cpp which was
already capped, so I left that alone.
git grep 'while (fuzz' should now run clean except for timedata.cpp
-BEGIN VERIFY SCRIPT-
# Rename
sed -i -e 's/MakeFuzzingContext/MakeNoLogFileContext/g' $(git grep -l MakeFuzzingContext)
# Bump the copyright of touched files in this scripted diff to avoid touching them again later
./contrib/devtools/copyright_header.py update ./src/test/fuzz/
-END VERIFY SCRIPT-
