py3: make scmposix.userrcpath() return bytes

We are making sure that we deal with bytes as much we can. This is a part
of fixing functions so that they return bytes if they have to.
Used encoding.environ to return bytes.

After this patch, scmposix.userrcpath() returns bytes and scmutil.osrcpath()
will also return bytes if the platform is posix. Functions is scmposix returns
bytes on Python 3 now.

mercurial/scmposix.py

@@ -1,39 +1,40 b''
 from __future__ import absolute_import
 
 import os
 import sys
 
 from . import (
+    encoding,
     osutil,
 )
 
 def _rcfiles(path):
     rcs = [os.path.join(path, 'hgrc')]
     rcdir = os.path.join(path, 'hgrc.d')
     try:
         rcs.extend([os.path.join(rcdir, f)
                     for f, kind in osutil.listdir(rcdir)
                     if f.endswith(".rc")])
     except OSError:
         pass
     return rcs
 
 def systemrcpath():
     path = []
     if sys.platform == 'plan9':
         root = 'lib/mercurial'
     else:
         root = 'etc/mercurial'
     # old mod_python does not set sys.argv
     if len(getattr(sys, 'argv', [])) > 0:
         p = os.path.dirname(os.path.dirname(sys.argv[0]))
         if p != '/':
             path.extend(_rcfiles(os.path.join(p, root)))
     path.extend(_rcfiles('/' + root))
     return path
 
 def userrcpath():
     if sys.platform == 'plan9':
-        return [os.environ['home'] + '/lib/hgrc']
+        return [encoding.environ['home'] + '/lib/hgrc']
     else:
         return [os.path.expanduser('~/.hgrc')]