commit: allow closing "non-head" changesets

Backout acd61dc44a39. The changeset prevented closing non-head changesets but
did not provide any rationale or test case and I don't see what value it adds.
Users might have their reasons to commit something anywhere - and close it
immediately.

And contrary to the comment that is removed: The topo heads set is _not_
included in the branch heads set of the current branch. It do not include
closed topological heads.

The change thus prevented closing commits on top of closing commits. A valid
usecase for that is to merge closed heads to reduce the number of topological
heads.

The only existing test coverage for this is the failing double close in
test-revset.t. It was added in 3cc2e34d7a7d and seems to not be intentional.

mercurial/commands.py

@@ -1299,10 +1299,6 b' def commit(ui, repo, *pats, **opts):'
 
     extra = {}
     if opts.get('close_branch'):
-        if repo['.'].node() not in repo.branchheads():
-            # The topo heads set is included in the branch heads set of the
-            # current branch, so it's sufficient to test branchheads
-            raise util.Abort(_('can only close branch heads'))
         extra['close'] = 1
 
     branch = repo[None].branch()

tests/test-branches.t

@@ -256,6 +256,27 b' verify update will accept invalid legacy'
   1 files updated, 0 files merged, 0 files removed, 0 files unresolved
   $ hg commit -d '9 0' --close-branch -m 'close this part branch too'
 
+  $ hg commit -d '9 0' --close-branch -m 're-closing this branch'
+  $ hg log -r tip --debug
+  changeset:   13:c2601d54b1427e99506bee25a566ef3a5963af0b
+  branch:      b
+  tag:         tip
+  phase:       draft
+  parent:      12:e3d49c0575d8fc2cb1cd6859c747c14f5f6d499f
+  parent:      -1:0000000000000000000000000000000000000000
+  manifest:    8:6f9ed32d2b310e391a4f107d5f0f071df785bfee
+  user:        test
+  date:        Thu Jan 01 00:00:09 1970 +0000
+  extra:       branch=b
+  extra:       close=1
+  description:
+  re-closing this branch
+  
+  
+  $ hg rollback
+  repository tip rolled back to revision 12 (undo commit)
+  working directory now based on revision 12
+
 --- b branch should be inactive
 
   $ hg branches

tests/test-revset.t

@@ -78,9 +78,6 b''
   $ hg branch all
   marked working directory as branch all
   (branches are permanent and global, did you want a bookmark?)
-  $ hg ci --close-branch -Aqm8
-  abort: can only close branch heads
-  [255]
 
   $ hg co 4
   0 files updated, 0 files merged, 0 files removed, 0 files unresolved