Fix accessing the repo through a symlink.

tests/test-symlink-root

@@ -0,0 +1,8 b''
+#!/bin/sh
+
+hg init a
+ln -s a link
+cd a
+echo foo > foo
+hg status
+hg status ../link

tests/test-symlink-root.out

@@ -0,0 +1,2 b''
+? foo
+? foo

mercurial/util.py

@@ -363,6 +363,9 b' def canonpath(root, cwd, myname):'
             except OSError:
                 break
             if samestat(name_st, root_st):
+                if not rel:
+                    # name was actually the same as root (maybe a symlink)
+                    return ''
                 rel.reverse()
                 name = os.path.join(*rel)
                 audit_path(name)