hg cat: accept changeset hashes

mercurial/commands.py

@@ -455,6 +455,13 b' def cat(ui, repo, file1, rev=None, **opt'
     """output the latest or given revision of a file"""
     r = repo.file(relpath(repo, [file1])[0])
     if rev:
+        try:
+            # assume all revision numbers are for changesets
+            n = repo.lookup(rev)
+            change = repo.changelog.read(n)
+            m = repo.manifest.read(change[0])
+            n = m[relpath(repo, [file1])[0]]
+        except hg.RepoError, KeyError:
         n = r.lookup(rev)
     else:
         n = r.tip()