merge: run _forgetremoved after manifestmerge

_forgetremoved can trigger manifest construction, but we only want it to
happen after manifestmerge, so that our attempt to read the manifests in the
right order in an upcoming patch actually works.

mercurial/merge.py

@@ -515,12 +515,12 b' def calculateupdates(repo, tctx, mctx, a'
             _checkcollision(mctx, None)
         else:
             _checkcollision(mctx, (tctx, ancestor))
-    if tctx.rev() is None:
-        actions += _forgetremoved(tctx, mctx, branchmerge)
     actions += manifestmerge(repo, tctx, mctx,
                              ancestor,
                              branchmerge, force,
                              partial)
+    if tctx.rev() is None:
+        actions += _forgetremoved(tctx, mctx, branchmerge)
     return actions
 
 def recordupdates(repo, actions, branchmerge):