Fix hg cat when the file cannot be found in the specified revision

mercurial/commands.py

@@ -579,8 +579,11 b' def cat(ui, repo, file1, rev=None, **opt'
             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)
+        except (hg.RepoError, KeyError):
+            try:
+                n = r.lookup(rev)
+            except KeyError, inst:
+                raise util.Abort('cannot find file %s in rev %s', file1, rev)
     else:
         n = r.tip()
     fp = make_file(repo, r, opts['output'], node=n)