python: Rework bytes/unicode string handling

python: Rework bytes/unicode string handling

In both Python 2 and 3, opening a file without specifying the mode will
open it for reading in text mode ('r').

On Python 2, the read() method of a file object opened in mode 'r' will
return byte strings, while on Python 3 it will return unicode strings.

Explicitly specifying the binary mode ('rb') then decoding the byte
string means we always handle unicode strings on both Python 2 and 3.

Which in turns means all re.match(line) will return unicode strings as
well.

If we also make expandCString return unicode strings, we don't need the
call to the unicode() constructor any more.

We were using the ugettext() method because it always returns unicode
strings in Python 2, contrarily to the gettext() one which returns
byte strings. The ugettext() method doesn't exist on Python 3, so we
must use the right method on each version of Python.

The last hurdles are that Python 3 doesn't let us concatenate unicode
and byte strings directly, and that Python 2's stdout wants encoded byte
strings while Python 3's want unicode strings.

With these changes, the script gives the same output on both Python 2
and 3.

Signed-off-by: Mathieu Bridon <bochecha@daitauha.fr>
Reviewed-by: Dylan Baker <dylan@pnwbakers.com>