subrepo: fix cloning of repos from urls without slash after host (issue2970)

This fixes a regression introduced with the new url handling in 1.9.

This should perhaps be fixed in the url class instead, but that might be too
invasive for a stable bugfix.

mercurial/subrepo.py

@@ -204,7 +204,7 b' def _abssource(repo, push=False, abort=T'
         parent = _abssource(repo._subparent, push, abort=False)
         if parent:
             parent = util.url(parent)
-            parent.path = posixpath.join(parent.path, source.path)
+            parent.path = posixpath.join(parent.path or '', source.path)
             parent.path = posixpath.normpath(parent.path)
             return str(parent)
     else: # recursion reached top repo

tests/test-http.t

@@ -159,6 +159,32 b' test http authentication'
 
   $ cd ..
 
+clone of serve with repo in root and unserved subrepo (issue2970)
+
+  $ hg --cwd test init sub
+  $ hg --cwd test/sub tag something
+  $ echo sub = sub > test/.hgsub
+  $ hg --cwd test add .hgsub
+  $ hg --cwd test commit -qm 'add subrepo'
+  $ hg clone http://localhost:$HGPORT noslash-clone
+  requesting all changes
+  adding changesets
+  adding manifests
+  adding file changes
+  added 3 changesets with 7 changes to 7 files
+  updating to branch default
+  abort: HTTP Error 404: Not Found
+  [255]
+  $ hg clone http://localhost:$HGPORT/ slash-clone
+  requesting all changes
+  adding changesets
+  adding manifests
+  adding file changes
+  added 3 changesets with 7 changes to 7 files
+  updating to branch default
+  abort: HTTP Error 404: Not Found
+  [255]
+
 check error log
 
   $ cat error.log