D3708: py3: replace `unicode` with `type(u'')` in isinstance() calls

[yuja (Yuya Nishihara)]

yuja added a comment.


  >   unicode() is not available on Python 3 and throws a NameError because unicodes
  >   are now default str() on py3.
  
  Appears that we need many `type(u'')`s, so I'd rather make `pycompat.unicode`
  available on both Py2 and Py3. IMHO, `type(u'')` is just a temporary
  workaround.

REPOSITORY
  rHG Mercurial

REVISION DETAIL
  https://phab.mercurial-scm.org/D3708

To: pulkit, #hg-reviewers
Cc: yuja, mercurial-devel