Merge branch 'lt/pathspec-negative'

The "negative" pathspec feature was somewhat more cumbersome to use
than necessary in that its short-hand used "!" which needed to be
escaped from shells, and it required "exclude from what?" specified.

* lt/pathspec-negative:
  pathspec: don't error out on all-exclusionary pathspec patterns
  pathspec magic: add '^' as alias for '!'