revlog: raise error.WdirUnsupported from revlog.node() if wdirrev is passed

When we try to run, 'hg debugrevspec 'branch(wdir())'', it throws an index error
and blows up. Lets raise the WdirUnsupported if wdir() is passed so that we can
catch that later.

mercurial/revlog.py

@@ -490,7 +490,12 b' class revlog(object):'
             raise
 
     def node(self, rev):
-        return self.index[rev][7]
+        try:
+            return self.index[rev][7]
+        except IndexError:
+            if rev == wdirrev:
+                raise error.WdirUnsupported
+            raise
 
     # Derived from index values.