Fix bzrlib.builtins.cmd_cat() output for pre 1.6.0 bzrlibs.

Fix bzrlib.builtins.cmd_cat() output for pre 1.6.0 bzrlibs.

Fixed in bzr.dev
  revno: 3341.2.1
  revision-id: bialix@ukr.net-20080407074826-5lwuyv4dn1qlijg4
  parent: pqm@pqm.ubuntu.com-20080407044456-s1a9orh0kssphdh9
  committer: Alexander Belchenko <bialix@ukr.net>
  branch nick: cmd-cat
  timestamp: Mon 2008-04-07 10:48:26 +0300
  message: `bzr cat` no more internally used Tree.print_file().
Merged into bzr.dev's trunk
  revno: 3512 [merge]
  revision-id: pqm@pqm.ubuntu.com-20080626004245-dnw85so4xqg8r9hy
  parent: pqm@pqm.ubuntu.com-20080625230724-lyux37pu8nx8tq34
  parent: aaron@aaronbentley.com-20080626001706-wo3w74fwgliy12s4
  committer: Canonical.com Patch Queue Manager <pqm@pqm.ubuntu.com>
  branch nick: +trunk
  timestamp: Thu 2008-06-26 01:42:45 +0100
  message: (bialix) Deprectate (Branch|Repository).print_file, fix cmd_cat

Before bzr branch 1.6
  bzr.dev$ bzr tags
  ...
  bzr-1.5rc1           3418.6.3
  bzr-1.6              3606.5.9
  ...

Fixes:

python test.py -q libbe.storage.vcs.bzr
...............................FSome value:1E..
======================================================================
ERROR: Get should be able to return the previous version.
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/wking/src/fun/be/be.wtk/libbe/storage/base.py", line 976, in test_
get_previous_version
    ret = self.s.get(self.id, revision=revs[i])
  File "/home/wking/src/fun/be/be.wtk/libbe/storage/base.py", line 335, in get
    value = self._get(*args, **kwargs)
  File "/home/wking/src/fun/be/be.wtk/libbe/storage/vcs/base.py", line 849, in _
get
    raise InvalidID(id, revision)
InvalidID: unlikely id in revision 1
...