Yep :-)  I am against throwing away valid data just because we can't
interpret it automatically.  Environment variables in Unix hold bytes. 
Those bytes are usually ASCii characters, however, they do not have to
be.  This is a case of being on the border between python and the
outside world so we need to be able to pass in bytes if the user
requests it.

Let's say that you have a local directory of: /home/\xff/username/bin in
your PATH environment variable and a command named my_app.sh in there. 
At the shell you can happily run myapp.sh and it will do it's thing. 
Now you open your python shell and do:
    subprocess.call(['myapp.sh'])

and it doesn't work.  This is non-intuitive behaviour for people who are
used to how the shell works.  All this patch will do is take away the
work around of subprocess.call(['bash', 'myapp.sh'])

"""
I tested Python 2.5: b is also removed, but Python 2.6 keeps the 
variable b.
"""
I just tested python-2.5.1 and b is kept, not removed.