push: refuse to push bumped changeset

This applies the same logic as used for `obsolete` and `unstable` changesets.
Refuse to push them without force.

We'll probably want to factor this logic with two new functions
`pctx.troubled()` and `ctx.troubles()`. But I'm waiting for the third
"trouble" to make it into core.

mercurial/localrepo.py

@@ -1872,6 +1872,7 b' class localrepository(object):'
                             # this message are here for 80 char limit reason
                             mso = _("push includes obsolete changeset: %s!")
                             msu = _("push includes unstable changeset: %s!")
+                            msb = _("push includes bumped changeset: %s!")
                             # If we are to push if there is at least one
                             # obsolete or unstable changeset in missing, at
                             # least one of the missinghead will be obsolete or
@@ -1882,6 +1883,8 b' class localrepository(object):'
                                     raise util.Abort(_(mso) % ctx)
                                 elif ctx.unstable():
                                     raise util.Abort(_(msu) % ctx)
+                                elif ctx.bumped():
+                                    raise util.Abort(_(msb) % ctx)
                         discovery.checkheads(self, remote, outgoing,
                                              remoteheads, newbranch,
                                              bool(inc))

tests/test-obsolete-checkheads.t

@@ -38,6 +38,7 b' New head replaces old head'
 ==========================
 
 setup
+(we add the 1 flags to prevent bumped error during the test)
 
   $ mkcommit old
   $ hg push
@@ -50,7 +51,7 b' setup'
   $ hg up -q '.^'
   $ mkcommit new
   created new head
-  $ hg debugobsolete `getid old` `getid new`
+  $ hg debugobsolete --flags 1 `getid old` `getid new`
   $ hg glog --hidden
   @  71e3228bffe1 (draft) add new
   |

tests/test-obsolete.t

@@ -171,6 +171,14 b' the public changeset'
   summary:     add new_3_c
   
 
+And that we can't push bumped changeset
+
+  $ hg push ../tmpa
+  pushing to ../tmpa
+  searching for changes
+  abort: push includes bumped changeset: 5601fb93a350!
+  [255]
+
 Fixing "bumped" situation
 We need to create a clone of 5 and add a special marker with a flag