changelog: make sure datafile is 00changelog.d (API)

0ad0d26ff7 makes it possible for changelog datafile to be "00changelog.i.d",
which is wrong. This patch adds an explicit datafile parameter to fix it.

mercurial/changelog.py

@@ -273,7 +273,9 b' class changelog(revlog.revlog):'
         else:
             indexfile = '00changelog.i'
 
-        revlog.revlog.__init__(self, opener, indexfile, checkambig=True)
+        datafile = '00changelog.d'
+        revlog.revlog.__init__(self, opener, indexfile, datafile=datafile,
+                               checkambig=True)
 
         if self._initempty:
             # changelogs don't benefit from generaldelta

mercurial/revlog.py

@@ -252,7 +252,7 b' class revlog(object):'
     If checkambig, indexfile is opened with checkambig=True at
     writing, to avoid file stat ambiguity.
     """
-    def __init__(self, opener, indexfile, checkambig=False):
+    def __init__(self, opener, indexfile, datafile=None, checkambig=False):
         """
         create a revlog object
 
@@ -260,7 +260,7 b' class revlog(object):'
         and can be used to implement COW semantics or the like.
         """
         self.indexfile = indexfile
-        self.datafile = indexfile[:-2] + ".d"
+        self.datafile = datafile or (indexfile[:-2] + ".d")
         self.opener = opener
         #  When True, indexfile is opened with checkambig=True at writing, to
         #  avoid file stat ambiguity.