This is a preparatory step for the next patch where we'll be fixing
strconv for Python2 builds with --enable-unicode=ucs2, where a unicode
character can be taking _2_ unicode points.

In that general case relying on unicode objects to represent runes is
not good, because many things generally do not work for U+10000 and
above, e.g. ord breaks:

    >>> import sys
    >>> sys.maxunicode
    65535                       <-- NOTE indicates UCS2 build
    >>> s = u'\U00012345'
    >>> s
    u'\U00012345'
    >>> s.encode('utf-8')
    '\xf0\x92\x8d\x85'
    >>> len(s)
    2                           <-- NOTE _not_ 1
    >>> ord(s)
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    TypeError: ord() expected a character, but string of length 2 found

so we switch to represent runes as integer, similarly to what Go does.