rename user_path_umountat() to user_path_mountpoint_at()

... and move the extern from linux/namei.h to fs/internal.h,
along with that of vfs_path_lookup().

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/internal.h

@@ -45,6 +45,9 @@ extern void __init chrdev_init(void);
  * namei.c
  */
 extern int __inode_permission(struct inode *, int);
+extern int user_path_mountpoint_at(int, const char __user *, unsigned int, struct path *);
+extern int vfs_path_lookup(struct dentry *, struct vfsmount *,
+			   const char *, unsigned int, struct path *);
 
 /*
  * namespace.c