obsolete: process markers in a stable order

Using set iteration order gave unstable debugsuccessorssets output with
PYTHONHASHSEED=random.

mercurial/obsolete.py

@@ -526,7 +526,7 b' def successorssets(repo, initialnode, ca'
             #   Having none means pruned node, multiple successors means split,
             #   single successors are standard replacement.
             #
-            for mark in succmarkers[current]:
+            for mark in sorted(succmarkers[current]):
                 for suc in mark[1]:
                     if suc not in cache:
                         if suc in stackedset:
@@ -563,7 +563,7 b' def successorssets(repo, initialnode, ca'
                 # duplicated entry and successors set that are strict subset of
                 # another one.
                 succssets = []
-                for mark in succmarkers[current]:
+                for mark in sorted(succmarkers[current]):
                     # successors sets contributed by this marker
                     markss = [[]]
                     for suc in mark[1]:

tests/test-obsolete-divergent.t

@@ -76,10 +76,10 b' A_1 have two direct and divergent succes'
   d20a80d4def3
       d20a80d4def3
   007dc284c1f8
+      82623d38b9ba
       392fd25390da
       82623d38b9ba
   82623d38b9ba
-      82623d38b9ba
   392fd25390da
       392fd25390da
   $ hg log -r 'divergent()'
@@ -123,10 +123,10 b' indirect divergence with known changeset'
   d20a80d4def3
       d20a80d4def3
   007dc284c1f8
+      82623d38b9ba
       01f36c5a8fda
       82623d38b9ba
   82623d38b9ba
-      82623d38b9ba
   392fd25390da
       01f36c5a8fda
   01f36c5a8fda
@@ -158,10 +158,10 b' indirect divergence with known changeset'
   d20a80d4def3
       d20a80d4def3
   007dc284c1f8
+      82623d38b9ba
       392fd25390da
       82623d38b9ba
   82623d38b9ba
-      82623d38b9ba
   392fd25390da
       392fd25390da
   $ hg log -r 'divergent()'