changegroupsubset: accept list of per-revlog nodes to include

This will allow strip to include in the temporary changegroup some extra
file/manifest revisions that should be restored after the truncations.

This code doesn't allow specification of changelog nodes since I won't
need that right now, the code wouldn't be tested and it's probably
possible to do something similar enough by using the bases/heads
arguments.

mercurial/localrepo.py

@@ -1510,7 +1510,7 b' class localrepository(repo.repository):'
             for node in nodes:
                 self.ui.debug("%s\n" % hex(node))
 
-    def changegroupsubset(self, bases, heads, source):
+    def changegroupsubset(self, bases, heads, source, extranodes=None):
         """This function generates a changegroup consisting of all the nodes
         that are descendents of any of the bases, and ancestors of any of
         the heads.
@@ -1520,7 +1520,15 b' class localrepository(repo.repository):'
         is non-trivial.
 
         Another wrinkle is doing the reverse, figuring out which changeset in
-        the changegroup a particular filenode or manifestnode belongs to."""
+        the changegroup a particular filenode or manifestnode belongs to.
+        
+        The caller can specify some nodes that must be included in the
+        changegroup using the extranodes argument.  It should be a dict
+        where the keys are the filenames (or 1 for the manifest), and the
+        values are lists of (node, linknode) tuples, where node is a wanted
+        node and linknode is the changelog node that should be transmitted as
+        the linkrev.
+        """
 
         self.hook('preoutgoing', throw=True, source=source)
 
@@ -1713,6 +1721,15 b' class localrepository(repo.repository):'
                 return msngset[fnode]
             return lookup_filenode_link
 
+        # Add the nodes that were explicitly requested.
+        def add_extra_nodes(name, nodes):
+            if not extranodes or name not in extranodes:
+                return
+
+            for node, linknode in extranodes[name]:
+                if node not in nodes:
+                    nodes[node] = linknode
+
         # Now that we have all theses utility functions to help out and
         # logically divide up the task, generate the group.
         def gengroup():
@@ -1728,6 +1745,7 b' class localrepository(repo.repository):'
             # The list of manifests has been collected by the generator
             # calling our functions back.
             prune_manifests()
+            add_extra_nodes(1, msng_mnfst_set)
             msng_mnfst_lst = msng_mnfst_set.keys()
             # Sort the manifestnodes by revision number.
             msng_mnfst_lst.sort(cmp_by_rev_func(mnfst))
@@ -1743,6 +1761,13 b' class localrepository(repo.repository):'
             msng_mnfst_lst = None
             msng_mnfst_set.clear()
 
+            if extranodes:
+                for fname in extranodes:
+                    if isinstance(fname, int):
+                        continue
+                    add_extra_nodes(fname,
+                                    msng_filenode_set.setdefault(fname, {}))
+                    changedfiles[fname] = 1
             changedfiles = changedfiles.keys()
             changedfiles.sort()
             # Go through all our files in order sorted by name.