commit in 'bzr shell' does not support non-ascii characters

(forwarded from Debian bug #542545 by Ben Finney)

When using ‘bzr shell’, I am unable to enter a commit message
containing non-ASCII characters:

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bzr burn.subprocess:119/> commit --message "Begin writing ‘get_media_info’ function."
Unhandled error:
'ascii' codec can't decode byte 0xe2 in position 14: ordinal not in range(128)
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If I then exit the shell in the same terminal, the same commit message
is handled fine:

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bzr burn.subprocess:119/> exit
$ bzr commit --message "Begin writing ‘get_media_info’ function."
Committing to: /home/bignose/Projects/burn/burn.subprocess/
modified changelog
modified burnlib/burn.py
modified burnlib/media.py
modified test/test_media.py
Please use create_signatures, not check_signatures to set signing policy.
Committed revision 120.
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Any characters accepted on the ‘bzr’ command line should be accepted
the same in ‘bzr shell’.