Added libbe/encoding.py to wrap input/output/file access appropriately.

Added libbe/encoding.py to wrap input/output/file access appropriately.

I borrowed most of the code for this.

get_encoding() is from Trac
  http://trac.edgewall.org/browser/trunk/trac/util/datefmt.py
  format_datetime()
Trac has a BSD license
  http://trac.edgewall.org/wiki/TracLicense
I don't know if such a small snippet requires us to "reproduce the
above copyright" or where we need to reproduce it if it is needed.

The stdout/stdin replacement code follows
  http://wiki.python.org/moin/ShellRedirectionFails

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).

References:
  http://wiki.python.org/moin/Unicode
  http://www.amk.ca/python/howto/unicode
  http://www.python.org/dev/peps/pep-0100/

I also split libbe/editor.py off from libbe.utility.py and started
explaining the motivation for the BugDir init flags in it's docstring.