tests/test-check-jshint.t

rust-status: traverse working directory in parallel

Using `rayon` for this task ensures that we are using the same work-stealing
threadpool for everything.

This change introduces `crossbeam` as an explicit dependency, although it is
already a dependency of `rayon`. It provides better structures for
multi-threaded tasks than the stdlib.

Differential Revision: https://phab.mercurial-scm.org/D8251

#require test-repo jshint hg10

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

run jshint on all tracked files ending in .js except vendored dependencies

  $ cd "`dirname "$TESTDIR"`"

  $ testrepohg locate 'set:**.js' \
  > 2>/dev/null \
  > | xargs jshint