push: perform bookmark export in the push function

This part is responsible for adding new bookmarks on the remote.  Before that,
it was done on its own in `commands.push`. The export is still not integrated
with the rest of the push process, but at least it now dwells in the right
function.

mercurial/commands.py

@@ -5074,11 +5074,10 b' def push(ui, repo, dest=None, **opts):'
 
     result = not pushop.cgresult
 
-    if opts.get('bookmark'):
-        bresult = bookmarks.pushtoremote(ui, repo, other, opts['bookmark'])
-        if bresult == 2:
+    if pushop.bkresult is not None:
+        if pushop.bkresult == 2:
             result = 2
-        elif not result and bresult:
+        elif not result and pushop.bkresult:
             result = 2
 
     return result

mercurial/exchange.py

@@ -216,6 +216,10 b' def push(repo, remote, force=False, revs'
         if locallock is not None:
             locallock.release()
 
+    if pushop.bookmarks:
+        pushop.bkresult = bookmod.pushtoremote(repo.ui, repo, remote,
+                                               pushop.bookmarks)
+
     return pushop
 
 # list of steps to perform discovery before push