transaction: pass the name of the "undo" journal to the transaction

It is time for the transaction to be responsible for setting up the
undo data. It is necessary to move this logic into the transaction
because many more files are handled now, and the transaction is the
object tracking them all.

The value can be set to None if no undo should be set.

mercurial/localrepo.py

@@ -912,6 +912,7 b' class localrepository(object):'
         vfsmap = {'plain': self.vfs} # root of .hg/
         tr = transaction.transaction(rp, self.svfs, vfsmap,
                                      "journal",
+                                     "undo",
                                      aftertrans(renames),
                                      self.store.createmode)
         # note: writing the fncache only during finalize mean that the file is

mercurial/transaction.py

@@ -82,8 +82,8 b' def _playback(journal, report, opener, v'
         pass
 
 class transaction(object):
-    def __init__(self, report, opener, vfsmap, journalname, after=None,
-                 createmode=None):
+    def __init__(self, report, opener, vfsmap, journalname, undoname=None,
+                 after=None, createmode=None):
         """Begin a new transaction
 
         Begins a new transaction that allows rolling back writes in the event of
@@ -105,6 +105,7 b' class transaction(object):'
         self.entries = []
         self.map = {}
         self.journal = journalname
+        self.undoname = undoname
         self._queue = []
         # a dict of arguments to be passed to hooks
         self.hookargs = {}