bundlerepo: use pathutil.normasprefix to ensure os.sep at the end of cwd

Since Python 2.7.9, "os.path.join(path, '')" doesn't add "os.sep" at
the end of UNC path (see issue4557 for detail).

This makes bundlerepo incorrectly work, if:

  1. cwd is the root of UNC share (e.g. "\host\share"), and
  2. mainreporoot is near cwd (e.g. "\host\sharefoo\repo")
     - host of UNC path is same as one of cwd
     - share of UNC path starts with one of cwd
  3. "repopath" isn't specified in bundle URI
     (e.g. "bundle:bundlefile" or just "bundlefile")

For example:

  $ hg --cwd \host\share -R \host\sharefoo\repo incoming bundle

In this case:

  - os.path.join(r"\host\share", "") returns r"\host\share",
  - r"\host\sharefoo\repo".startswith(r"\host\share") returns True, then
  - r"foo\repo" is treated as repopath of bundlerepo instead of
    r"\host\sharefoo\repo"

This causes failure of combining "\host\sharefoo\repo" and bundle
file: in addition to it, "\host\share\foo\repo" may be combined with
bundle file, if it accidentally exists.

This patch uses "pathutil.normasprefix()" to ensure "os.sep" at the
end of cwd safely, even with some problematic encodings, which use
0x5c (= "os.sep" on Windows) as the tail byte of some multi-byte
characters.

BTW, normalization before "pathutil.normasprefix()" isn't needed in
this case, because "os.getcwd()" always returns normalized one.

mercurial/bundlerepo.py

@@ -16,6 +16,7 b' from i18n import _'
 import os, tempfile, shutil
 import changegroup, util, mdiff, discovery, cmdutil, scmutil, exchange
 import localrepo, changelog, manifest, filelog, revlog, error, phases, bundle2
+import pathutil
 
 class bundlerevlog(revlog.revlog):
     def __init__(self, opener, indexfile, bundle, linkmapper):
@@ -352,7 +353,7 b' def instance(ui, path, create):'
         if parentpath == cwd:
             parentpath = ''
         else:
-            cwd = os.path.join(cwd,'')
+            cwd = pathutil.normasprefix(cwd)
             if parentpath.startswith(cwd):
                 parentpath = parentpath[len(cwd):]
     u = util.url(path)