discovery: fix regression when checking heads for pre 1.4 client (issue3218)

This code is not run by the test suite and silly name error were lurking here.

mercurial/discovery.py

@@ -131,7 +131,7 b' def findcommonoutgoing(repo, other, only'
 
     return og
 
-def checkheads(repo, remote, outgoing, remoteheads, newbranch=False):
+def checkheads(repo, remote, outgoing, remoteheads, newbranch=False, inc=False):
     """Check that a push won't add any outgoing head
 
     raise Abort error and display ui message as needed.
@@ -190,9 +190,9 b' def checkheads(repo, remote, outgoing, r'
         # Construct {old,new}map with branch = None (topological branch).
         # (code based on _updatebranchcache)
         oldheads = set(h for h in remoteheads if h in cl.nodemap)
-        newheads = oldheads.union(outg)
+        newheads = oldheads.union(outgoing.missing)
         if len(newheads) > 1:
-            for latest in reversed(outg):
+            for latest in reversed(outgoing.missing):
                 if latest not in newheads:
                     continue
                 minhrev = min(cl.rev(h) for h in newheads)

mercurial/localrepo.py

@@ -1635,7 +1635,8 b' class localrepository(repo.repository):'
                     # something to push
                     if not force:
                         discovery.checkheads(self, remote, outgoing,
-                                             remoteheads, newbranch)
+                                             remoteheads, newbranch,
+                                             bool(inc))
 
                     # create a changegroup from local
                     if revs is None and not outgoing.excluded: