subrepo: make -S work again on Windows for incoming/outgoing to remote repos

While it worked fine for the top level repo, the remote path for the subrepo got
mangled to something like "https://server/prefix\repo\subrepo", which I've seen
result in both a 400 and a 404, depending on the server.  We need to `normpath`
at least the `subpath` because of "http://user:***@localhost:$HGPORT/main/../sub"
in `test-subrepo-relative-path.t`.  Keep the `os.path` flavor for handling
filesystem based remote repos, since this string is also displayed.

This is one case where the automatic substitution of '\' for '/' and rematching
done by the test runner is unfortunate- I don't see how to write a test to catch
this.

Differential Revision: https://phab.mercurial-scm.org/D11971

mercurial/hg.py

@@ -10,6 +10,7 b' from __future__ import absolute_import'
 
 import errno
 import os
+import posixpath
 import shutil
 import stat
 import weakref
@@ -1292,7 +1293,11 b' def _incoming('
             source = bytes(subpath)
         else:
             p = urlutil.url(source)
-            p.path = os.path.normpath(b'%s/%s' % (p.path, subpath))
+            if p.islocal():
+                normpath = os.path.normpath
+            else:
+                normpath = posixpath.normpath
+            p.path = normpath(b'%s/%s' % (p.path, subpath))
             source = bytes(p)
     other = peer(repo, opts, source)
     cleanupfn = other.close
@@ -1363,7 +1368,11 b' def _outgoing(ui, repo, dests, opts, sub'
                 dest = bytes(subpath)
             else:
                 p = urlutil.url(dest)
-                p.path = os.path.normpath(b'%s/%s' % (p.path, subpath))
+                if p.islocal():
+                    normpath = os.path.normpath
+                else:
+                    normpath = posixpath.normpath
+                p.path = normpath(b'%s/%s' % (p.path, subpath))
                 dest = bytes(p)
         branches = path.branch, opts.get(b'branch') or []