`tahoe status` explodes on an encoding issue in some environments

[exarkun]

If you have a recent operation on a client node then:

LANG=C tahoe status

explodes thusly:

Statistics (for last 37 seconds):
    uploaded 3.31 MB in 1 files
  downloaded 0 B in 0 files

No active operations.

Recent operations:
Traceback (most recent call last):
  File "/nix/store/knrv5c2qzbxrr7f6hp5xj9zgcig36j3w-python-2.7.17/lib/python2.7/threading.py", line 801, in __bootstrap_inner
    self.run()
  File "/nix/store/knrv5c2qzbxrr7f6hp5xj9zgcig36j3w-python-2.7.17/lib/python2.7/threading.py", line 754, in run
    self.__target(*self.__args, **self.__kwargs)
  File "/home/exarkun/VirtualEnvs/tahoe-lafs/lib/python2.7/site-packages/twisted/_threads/_threadworker.py", line 46, in work
    task()
  File "/home/exarkun/VirtualEnvs/tahoe-lafs/lib/python2.7/site-packages/twisted/_threads/_team.py", line 190, in doWork
    task()
--- <exception caught here> ---
  File "/home/exarkun/VirtualEnvs/tahoe-lafs/lib/python2.7/site-packages/twisted/python/threadpool.py", line 250, in inContext
    result = inContext.theWork()
  File "/home/exarkun/VirtualEnvs/tahoe-lafs/lib/python2.7/site-packages/twisted/python/threadpool.py", line 266, in <lambda>
    inContext.theWork = lambda: context.call(ctx, func, *args, **kw)
  File "/home/exarkun/VirtualEnvs/tahoe-lafs/lib/python2.7/site-packages/twisted/python/context.py", line 122, in callWithContext
    return self.currentContext().callWithContext(ctx, func, *args, **kw)
  File "/home/exarkun/VirtualEnvs/tahoe-lafs/lib/python2.7/site-packages/twisted/python/context.py", line 85, in callWithContext
    return func(*args,**kw)
  File "/home/exarkun/Work/python/tahoe-lafs/src/allmydata/scripts/cli.py", line 595, in status
    return tahoe_status.do_status(options)
  File "/home/exarkun/Work/python/tahoe-lafs/src/allmydata/scripts/tahoe_status.py", line 296, in do_status
    render_recent(options['verbose'], options.stdout, status_data)
  File "/home/exarkun/Work/python/tahoe-lafs/src/allmydata/scripts/tahoe_status.py", line 239, in render_recent
    print(header, file=stdout)
exceptions.UnicodeEncodeError: 'ascii' codec can't encode character u'\u2553' in position 0: ordinal not in range(128)

[exarkun]

The test coverage for for tahoe status fakes tons of stuff, including stdout, so it can't catch this.