rust: run a clippy pass with the latest stable version
Our current version of clippy is older than the latest stable.
The newest version has new lints that are moslty good advice, so let's apply
them ahead of time. This has the added benefit of reducing the noise for
developpers like myself that use clippy as an IDE helper, as well as being
more prepared for a future clippy upgrade.
cat >> $HGRCPATH <<EOF
[extensions]
narrow=
[experimental]
changegroup3 = True
EOF