subrepo: use code from 71ea5b2b9517 only if Python needs it (issue2795)

With Python >= 2.6 the original code already works correct, therefore the
fix for issue2556 on Python <= 2.5 broke relative subrepositories with
newer versions of Python.

mercurial/subrepo.py

@@ -203,7 +203,8 b' def _abssource(repo, push=False, abort=T'
                 if parent[-1] == '/':
                     parent = parent[:-1]
                 r = urlparse.urlparse(parent + '/' + source)
-                if parent.startswith('ssh://'):
+                if parent.startswith('ssh://') and not r[1]:
+                    # Python before 2.6 parses ssh:// URLs wrong
                     host, path = r[2][2:].split('/', 1)
                     r2 = '//%s/%s' % (host, posixpath.normpath(path))
                 else: