py3: traceback upon running vdiff

Created originally on Bitbucket by cbillington (Chris Billington)

I'm on Arch Linux with a development build of mercurial and a custom package for installing tortoisehg for python 3. Arch is rapidly dropping Python 2 components, and it's getting harder to keep the required Python 2 components around for thg. So I'm running it on Python 3 - it's hitting many issues but I'm just going to report them all and hopefully things will be in shape at some point!

Here's what I get when I run thg vdiff <some_file>

  #!python
    ** Mercurial version (5.2+86-a78a65c33b5a).  TortoiseHg version (5.1+189-2660c64eacb4)
    ** Command: vdiff /home/bilbo/labscript_suite/userlib/pythonlib/alkali/atom.py
    ** CWD: /home/bilbo/labscript_suite/userlib/pythonlib/alkali
    ** Encoding: UTF-8
    ** Extensions loaded: strip, mq, churn, rebase, tortoisehg.util.configitems
    ** Python version: 3.7.4 (default, Oct  4 2019, 06:57:26) [GCC 9.2.0]
    ** System: Linux bilbo-arch 4.19.83-1-lts #1 SMP Sun, 10 Nov 2019 11:29:44 +0000 x86_64
    ** Qt-5.13.2 PyQt-5.13.2 QScintilla-2.11.3
    Traceback (most recent call last):
      File "/usr/lib/python3.7/site-packages/tortoisehg/hgqt/run.py", line 138, in dispatch
        return _runcatch(u, args)
      File "/usr/lib/python3.7/site-packages/tortoisehg/hgqt/run.py", line 342, in _runcatch
        return runcommand(ui, args)
      File "/usr/lib/python3.7/site-packages/tortoisehg/hgqt/run.py", line 435, in runcommand
        return _runcommand(lui, options, cmd, d)
      File "/usr/lib/python3.7/site-packages/tortoisehg/hgqt/run.py", line 487, in _runcommand
        return checkargs()
      File "/usr/lib/python3.7/site-packages/tortoisehg/hgqt/run.py", line 440, in checkargs
        return cmdfunc()
      File "/usr/lib/python3.7/site-packages/tortoisehg/hgqt/run.py", line 434, in <lambda>
        **pycompat.strkwargs(cmdoptions))
      File "/usr/lib/python3.7/site-packages/tortoisehg/hgqt/qtapp.py", line 464, in __call__
        dlg, reporoot = self._createdialog(dlgfunc, args, opts)
      File "/usr/lib/python3.7/site-packages/tortoisehg/hgqt/qtapp.py", line 528, in _createdialog
        return dlgfunc(self._ui, *args, **opts), reporoot
      File "/usr/lib/python3.7/site-packages/mercurial/util.py", line 1843, in check
        return func(*args, **kwargs)
      File "/usr/lib/python3.7/site-packages/tortoisehg/hgqt/run.py", line 1417, in vdiff
        pats = hglib.canonpaths(pats)
      File "/usr/lib/python3.7/site-packages/tortoisehg/util/hglib.py", line 379, in canonpaths
        canonpats.append(pathutil.canonpath(root, cwd, f))
      File "/usr/lib/python3.7/site-packages/mercurial/pathutil.py", line 191, in canonpath
        if util.endswithsep(root):
      File "/usr/lib/python3.7/site-packages/mercurial/util.py", line 2271, in endswithsep
        path.endswith(pycompat.ossep)
    TypeError: endswith first arg must be str or a tuple of str, not bytes