core: don't hard-code node length

Differential Revision: https://phab.mercurial-scm.org/D10536

mercurial/localrepo.py

@@ -1840,7 +1840,7 b' class localrepository(object):'
                 # when we know that '.' won't be hidden
                 node = self.dirstate.p1()
                 rev = self.unfiltered().changelog.rev(node)
-            elif len(changeid) == 20:
+            elif len(changeid) == self.nodeconstants.nodelen:
                 try:
                     node = changeid
                     rev = self.changelog.rev(changeid)

mercurial/revlog.py

@@ -1299,7 +1299,7 b' class revlog(object):'
         if isinstance(id, int):
             # rev
             return self.node(id)
-        if len(id) == 20:
+        if len(id) == self.nodeconstants.nodelen:
             # possibly a binary node
             # odds of a binary node being all hex in ASCII are 1 in 10**25
             try: