obsolete: test an important corner case

Receiving markers affecting changeset we'll receives later is legitimate and
not so uncommon case. Working on cache highlighted that this was only testing
in the evolve extension. We add a test for this case in core.

tests/test-obsolete.t

@@ -1280,5 +1280,36 b' Test the --delete option of debugobsolet'
   $ hg debugobsolete
   cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b f9bd49731b0b175e42992a3c8fa6c678b2bc11f1 0 \(.*\) {'user': 'test'} (re)
   1ab51af8f9b41ef8c7f6f3312d4706d870b1fb74 29346082e4a9e27042b62d2da0e2de211c027621 0 \(.*\) {'user': 'test'} (re)
+
+Test adding changeset after obsmarkers affecting it
+(eg: during pull, or unbundle)
+
+  $ mkcommit e
+  $ hg bundle -r . --base .~1 ../bundle-2.hg
+  1 changesets found
+  $ getid .
+  $ hg --config extensions.strip= strip -r .
+  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
+  saved backup bundle to $TESTTMP/tmpe/issue4845/doindexrev/.hg/strip-backup/9bc153528424-ee80edd4-backup.hg (glob)
+  $ hg debugobsolete 9bc153528424ea266d13e57f9ff0d799dfe61e4b
+  $ hg unbundle ../bundle-2.hg
+  adding changesets
+  adding manifests
+  adding file changes
+  added 1 changesets with 1 changes to 1 files
+  (run 'hg update' to get a working copy)
+  $ hg log -G
+  @  7:7ae79c5d60f0 (draft) [tip ] dd
+  |
+  | o  6:4715cf767440 (draft) [ ] d
+  |/
+  o  5:29346082e4a9 (draft) [ ] cc
+  |
+  o  3:d27fb9b06607 (draft) [ ] bb
+  |
+  | o  2:6fdef60fcbab (draft) [ ] b
+  |/
+  o  1:f9bd49731b0b (draft) [ ] aa
+  
+
   $ cd ..
-