Renamed test->manipulate_encodings in becommands.*.execute.

Renamed test->manipulate_encodings in becommands.*.execute.

Reminder from my initial libbe/encoding.py commit:
  Because of the stdout replacement, the doctests executes now need an
  optional 'test' argument to turn off replacement during the doctests,
  otherwise doctest flips out (since it had set up stdout to catch
  output, and then we clobbered it's setup).

I'm also trying to catch stdout/stderr from be-handle-mail, and I ran
into the same problem.  It took me a bit to remember exactly what
"test" was supposed to do, so I thought I'd make the argument name
more specific.  If you need other changes when running in "test" mode,
you'll have to add other kwargs.