push: move changeset push logic in its own function

Now that every necessary information is held in the `pushoperation` object, we
can extract the logic pushing changeset  to it's own function.

This changeset is pure code movement only.

mercurial/exchange.py

@@ -141,7 +141,23 b' def push(repo, remote, force=False, revs'
                     discovery.checkheads(unfi, pushop.remote, outgoing,
                                          remoteheads, pushop.newbranch,
                                          bool(inc), newbm)
+                _pushchangeset(pushop)
+            _pushsyncphase(pushop)
+            _pushobsolete(pushop)
+        finally:
+            if lock is not None:
+                lock.release()
+    finally:
+        if locallock is not None:
+            locallock.release()
 
+    _pushbookmark(pushop)
+    return pushop.ret
+
+def _pushchangeset(pushop):
+    """Make the actual push of changeset bundle to remote repo"""
+    outgoing = pushop.outgoing
+    unbundle = pushop.remote.capable('unbundle')
                 # TODO: get bundlecaps from remote
                 bundlecaps = None
                 # create a changegroup from local
@@ -155,8 +171,7 b' def push(repo, remote, force=False, revs'
                                                         'push',
                                                         fastpath=True)
                 else:
-                    cg = pushop.repo.getlocalbundle('push', outgoing,
-                                                    bundlecaps)
+        cg = pushop.repo.getlocalbundle('push', outgoing, bundlecaps)
 
                 # apply changegroup to remote
                 if unbundle:
@@ -178,18 +193,6 b' def push(repo, remote, force=False, revs'
                     pushop.ret = pushop.remote.addchangegroup(cg, 'push',
                                                               pushop.repo.url())
 
-            _pushsyncphase(pushop)
-            _pushobsolete(pushop)
-        finally:
-            if lock is not None:
-                lock.release()
-    finally:
-        if locallock is not None:
-            locallock.release()
-
-    _pushbookmark(pushop)
-    return pushop.ret
-
 def _pushsyncphase(pushop):
     """synchronise phase information locally and remotly"""
     unfi = pushop.repo.unfiltered()