revlog: pass node as an argument of addrevision

This change will allow revlog subclasses that override 'checkhash' method
to use custom strategy of computing nodeids without overriding 'addrevision'
method. In particular this change is necessary to implement manifest
compression.

mercurial/revlog.py

@@ -993,7 +993,8 b' class revlog(object):'
         tr.replace(self.indexfile, trindex * self._io.size)
         self._chunkclear()
 
-    def addrevision(self, text, transaction, link, p1, p2, cachedelta=None):
+    def addrevision(self, text, transaction, link, p1, p2, cachedelta=None,
+                    node=None):
         """add a revision to the log
 
         text - the revision data to add
@@ -1001,11 +1002,14 b' class revlog(object):'
         link - the linkrev data to add
         p1, p2 - the parent nodeids of the revision
         cachedelta - an optional precomputed delta
+        node - nodeid of revision; typically node is not specified, and it is
+            computed by default as hash(text, p1, p2), however subclasses might
+            use different hashing method (and override checkhash() in such case)
         """
         if link == nullrev:
             raise RevlogError(_("attempted to add linkrev -1 to %s")
                               % self.indexfile)
-        node = hash(text, p1, p2)
+        node = node or hash(text, p1, p2)
         if node in self.nodemap:
             return node