tests/test-check-rust-format.t

graft: use revset for intersecting with ancestor set

This addresses a TODO added in a1381eea7c7d (graft: do not use
`.remove` on a smart set (regression), 2014-04-28).

Differential Revision: https://phab.mercurial-scm.org/D7806

#require rustfmt test-repo

  $ . "$TESTDIR/helpers-testrepo.sh"

  $ cd "$TESTDIR"/..
  $ RUSTFMT=$(rustup which --toolchain nightly rustfmt)
  $ for f in `testrepohg files 'glob:**/*.rs'` ; do
  >   $RUSTFMT --check --unstable-features --color=never $f
  > done