dirstate: don't use actualfilename to name the backup file

The issue with using actualfilename is that dirstate saved during transaction
with "pending" in filename will be impossible to recover from outside of the
transaction because the recover method will be looking for the name without
"pending".

mercurial/dirstate.py

@@ -1230,7 +1230,7 b' class dirstate(object):'
             # end of this transaction
             tr.registertmp(filename, location='plain')
 
-        self._opener.write(prefix + filename + suffix,
+        self._opener.write(prefix + self._filename + suffix,
                            self._opener.tryread(filename))
 
     def restorebackup(self, tr, suffix='', prefix=''):
@@ -1239,9 +1239,10 b' class dirstate(object):'
         # changes of dirstate out after restoring from backup file
         self.invalidate()
         filename = self._actualfilename(tr)
-        self._opener.rename(prefix + filename + suffix, filename)
+        # using self._filename to avoid having "pending" in the backup filename
+        self._opener.rename(prefix + self._filename + suffix, filename)
 
     def clearbackup(self, tr, suffix='', prefix=''):
         '''Clear backup file with suffix'''
-        filename = self._actualfilename(tr)
-        self._opener.unlink(prefix + filename + suffix)
+        # using self._filename to avoid having "pending" in the backup filename
+        self._opener.unlink(prefix + self._filename + suffix)