upgrade: clarify "aggressivemergedelta" handling

We rename "aggressivemergedelta" argument to "forceaggressivemergedelta". The
previous argument naming could infer an absolute control on the behavior.
However, the code show we respect the config option if set.

mercurial/revlog.py

@@ -2287,7 +2287,7 b' class revlog(object):'
     DELTAREUSEALL = {'always', 'samerevs', 'never', 'fulladd'}
 
     def clone(self, tr, destrevlog, addrevisioncb=None,
-              deltareuse=DELTAREUSESAMEREVS, deltabothparents=None):
+              deltareuse=DELTAREUSESAMEREVS, forcedeltabothparents=None):
         """Copy this revlog to another, possibly with format changes.
 
         The destination revlog will contain the same revisions and nodes.
@@ -2321,9 +2321,9 b' class revlog(object):'
         deltas will be recomputed if the delta's parent isn't a parent of the
         revision.
 
-        In addition to the delta policy, the ``deltabothparents`` argument
-        controls whether to compute deltas against both parents for merges.
-        By default, the current default is used.
+        In addition to the delta policy, the ``forcedeltabothparents``
+        argument controls whether to force compute deltas against both parents
+        for merges. By default, the current default is used.
         """
         if deltareuse not in self.DELTAREUSEALL:
             raise ValueError(_('value for deltareuse invalid: %s') % deltareuse)
@@ -2346,7 +2346,7 b' class revlog(object):'
             elif deltareuse == self.DELTAREUSESAMEREVS:
                 destrevlog._lazydeltabase = False
 
-            destrevlog._deltabothparents = deltabothparents or oldamd
+            destrevlog._deltabothparents = forcedeltabothparents or oldamd
 
             populatecachedelta = deltareuse in (self.DELTAREUSEALWAYS,
                                                 self.DELTAREUSESAMEREVS)

mercurial/upgrade.py

@@ -456,7 +456,7 b' def _revlogfrompath(repo, path):'
         #reverse of "/".join(("data", path + ".i"))
         return filelog.filelog(repo.svfs, path[5:-2])
 
-def _copyrevlogs(ui, srcrepo, dstrepo, tr, deltareuse, deltabothparents):
+def _copyrevlogs(ui, srcrepo, dstrepo, tr, deltareuse, forcedeltabothparents):
     """Copy revlogs between 2 repos."""
     revcount = 0
     srcsize = 0
@@ -578,7 +578,7 b' def _copyrevlogs(ui, srcrepo, dstrepo, t'
         ui.note(_('cloning %d revisions from %s\n') % (len(oldrl), unencoded))
         oldrl.clone(tr, newrl, addrevisioncb=oncopiedrevision,
                     deltareuse=deltareuse,
-                    deltabothparents=deltabothparents)
+                    forcedeltabothparents=forcedeltabothparents)
 
         info = newrl.storageinfo(storedsize=True)
         datasize = info['storedsize'] or 0