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
https://bz.mercurial-scm.org/619
$ hg init
$ echo a > a
$ hg ci -Ama
adding a
$ echo b > b
$ hg branch b
marked working directory as branch b
(branches are permanent and global, did you want a bookmark?)
$ hg ci -Amb
adding b
$ hg co -C 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
Fast-forward:
$ hg merge b
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ hg ci -Ammerge
Bogus fast-forward should fail:
$ hg merge b
abort: merging with a working directory ancestor has no effect
[255]
Even with strange revset (issue4465)
$ hg merge ::.
abort: merging with a working directory ancestor has no effect
[255]