[MERGE] Implementation and tests for -r revno:N:path

[Aaron Bentley]

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+        except NotBranchError:
+            # Don't raise an error when bzr diff is called from
+            # outside a working tree.
+            tree1, tree2 = None, None

This patch causes us to get a very bad error when plain 'bzr diff' is
run in an unversioned directory:

AttributeError: 'NoneType' object has no attribute 'basis_tree'

Previously, it produced:

bzr: ERROR: Not a branch: /home/abentley/bzrplugins/

I'd consider this a regression.

Aaron
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