unique/missing revisions tabs should catch NotBranchError

[Alexander Belchenko]

I've deleted parent branch for some branch. Now, when I'm open Unique/Missing Revisions tabs I see "Fetching..." there and traceback in the console:

Traceback (most recent call last):
  File "C:\work\Bazaar\plugins\explorer\lib\explorer.py", line 902, in callable_
with_cleanup
    task_callable()
  File "C:\work\Bazaar\plugins\explorer\lib\view_repository.py", line 316, in ta
sk
    text = extra_revisions_as_html(self.branch)
  File "C:\work\Bazaar\plugins\explorer\lib\html_extras.py", line 46, in extra_r
evisions_as_html
    parent_branch = Branch.open(parent)
  File "bzrlib\branch.pyo", line 136, in open
  File "bzrlib\bzrdir.pyo", line 837, in open
  File "bzrlib\bzrdir.pyo", line 867, in open_from_transport
  File "bzrlib\transport\__init__.pyo", line 1642, in do_catching_redirections
  File "bzrlib\bzrdir.pyo", line 854, in find_format
  File "bzrlib\bzrdir.pyo", line 1789, in find_format
bzrlib.errors.NotBranchError: Not a branch: "C:/work/Bazaar/repos/qbzr-repo-1.9/
revno.769/".

[Ian Clatworthy (ian-clatworthy)]

Fix committed in rev 183.