Convert sys.argv to Unicode (using a configurable encoding)

Convert sys.argv to Unicode (using a configurable encoding)

In Python 3, sys.argv is already Unicode, but there's no clean way to
do this automatically in Python 2 [1].  If your system doesn't use
UTF-8 for it's argv encoding, you should set system.argv-encoding in
your ~/.mutt-ldap.rc.  For example, if your system uses UTF-16, try:

  [system]
  argv-encoding = utf-16

[1]: http://bugs.python.org/issue2128