Incorporate documentation and naming feedback gotten for r1554800.
No functional change.

* subversion/include/svn_fs.h
  (svn_fs_node_relation_t): Add references to the values previously
                            used for these relations.  Fix member
                            spelling and docstring typos.
  (svn_fs_node_relation): Just declare the current behavior as the
                          intended one.

* subversion/libsvn_fs_base/tree.c
  (base_node_relation): Adapt to enum member spelling fix.

* subversion/libsvn_fs_fs/tree.c
  (fs_node_relation): Ditto.

* subversion/libsvn_fs_x/tree.c
  (x_node_relation): Ditto.

Suggested by: julianfoad


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1574038 13f79535-47bb-0310-9956-ffa450edef68
* subversion/libsvn_fs/fs-loader.c
  (svn_fs_node_relation):  As we recently defined different FS instances
                           to imply unrelated notes, we can replace the
                           somewhat fragile vtable check with a stricter
                           FS comparison.

Suggested by: julianfoad

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1574056 13f79535-47bb-0310-9956-ffa450edef68