tests/test-empty-dir.t

exchange: move simple narrow changegroup generation from extension

The narrow extension completely replaced the function generating the
changegroup part when a narrow changegroup was requested. Previous
commits have taught the in-core changegroup code how to filter files
based on a matcher. This commit teaches the in-core bundle2 part
generation code to construct a matcher based on arguments. It
will also emit a bundle2 part describing the narrow spec.

I believe the changegroup part generation code in the narrow extension
is now limited to ellipsis serving mode. i.e. core is now capable
of narrow changegroup generation when ellipsis mode is disabled.

Differential Revision: https://phab.mercurial-scm.org/D4014

  $ hg init

  $ echo 123 > a
  $ hg add a
  $ hg commit -m "first" a

  $ mkdir sub
  $ echo 321 > sub/b
  $ hg add sub/b
  $ hg commit -m "second" sub/b

  $ cat sub/b
  321

  $ hg co 0
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved

  $ cat sub/b 2>/dev/null || echo "sub/b not present"
  sub/b not present

  $ test -d sub || echo "sub not present"
  sub not present