revlog: make 'storedeltachains' a "public" attribute

The next changeset will make that attribute read by the changegroup packer. We
make it "public" beforehand.

mercurial/changelog.py

@@ -267,7 +267,7 b' class changelog(revlog.revlog):'
         # Delta chains for changelogs tend to be very small because entries
         # tend to be small and don't delta well with each. So disable delta
         # chains.
-        self._storedeltachains = False
+        self.storedeltachains = False
 
         self._realopener = opener
         self._delayed = False

mercurial/revlog.py

@@ -297,7 +297,7 b' class revlog(object):'
             raise RevlogError(_("index %s unknown format %d")
                               % (self.indexfile, fmt))
 
-        self._storedeltachains = True
+        self.storedeltachains = True
 
         self._io = revlogio()
         if self.version == REVLOGV0:
@@ -1471,7 +1471,7 b' class revlog(object):'
             textlen = len(text)
 
         # should we try to build a delta?
-        if prev != nullrev and self._storedeltachains:
+        if prev != nullrev and self.storedeltachains:
             tested = set()
             # This condition is true most of the time when processing
             # changegroup data into a generaldelta repo. The only time it