tests/test-merge-revert.t

graftcopies: use _filter() for filtering out invalid copies

`graftcopies()` (formerly called `duplicatecopies()`) checked that the
copy destination existed in the working copy, but it didn't check that
copy source existed in the parent of the working copy. In
`test-graft.t` we can see that as warnings about not finding ancestors
of the copied files, and also empty commits getting created.

This patch uses the existing `_filter()` function for filtering out
invalid copies. In addition to the aforementioned types, that also
includes copies where source and destination is the same.

Differential Revision: https://phab.mercurial-scm.org/D7859

  $ hg init

  $ echo "added file1" > file1
  $ echo "added file2" > file2
  $ hg add file1 file2
  $ hg commit -m "added file1 and file2"

  $ echo "changed file1" >> file1
  $ hg commit -m "changed file1"

  $ hg -q log
  1:08a16e8e4408
  0:d29c767a4b52
  $ hg id
  08a16e8e4408 tip

  $ hg update -C 0
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg id
  d29c767a4b52
  $ echo "changed file1" >> file1
  $ hg id
  d29c767a4b52+

  $ hg revert --all
  reverting file1
  $ hg diff
  $ hg status
  ? file1.orig
  $ hg id
  d29c767a4b52

  $ hg update
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg diff
  $ hg status
  ? file1.orig
  $ hg id
  08a16e8e4408 tip

  $ hg update -C 0
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ echo "changed file1" >> file1

  $ hg update
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg diff
  $ hg status
  ? file1.orig
  $ hg id
  08a16e8e4408 tip

  $ hg revert --all
  $ hg diff
  $ hg status
  ? file1.orig
  $ hg id
  08a16e8e4408 tip

  $ hg revert -r tip --all
  $ hg diff
  $ hg status
  ? file1.orig
  $ hg id
  08a16e8e4408 tip

  $ hg update -C
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg diff
  $ hg status
  ? file1.orig
  $ hg id
  08a16e8e4408 tip