Bindings for dump stream parser

Hi all,

Please review/comment.

[[[
Implement Python bindings for dump stream parser.

* subversion/bindings/swig/include/svn_types.swg
   (): Fix a typo in svn_repos_parser_fns2_t type name, add
   svn_repos_parser_fns2_t type to the argout typemap.

* subversion/bindings/swig/python/libsvn_swig_py/swigutil_py.c
   (item_baton): Add pool; needed for certain methods in dump
   stream parser that do not take pool argument.
   (make_baton): Increment refcount on `editor'; remove incorrect
   the comment stating the current usage is safe. Save pool pointer.
   (close_baton): Decrement refcount on `editor'.
   (svn_swig_py_make_parse_fns3): New function; creates vtable/baton
   to be used in a later call to repos.parse_dumpstream3()

* subversion/bindings/swig/python/libsvn_swig_py/swigutil_py.h:
   (svn_swig_py_make_parse_fns3): New function.

* subversion/bindings/swig/python/svn/core.py
   (Stream.close): Guard against double-close.

* subversion/bindings/swig/python/svn/repos.py
   (ParseFns3): New class; vtable for dump stream parser.

* subversion/bindings/swig/python/tests/repository.py
   (test_parse_fns3): Test for dump stream parser bindings.
   (test_unnamed_editor): Test delta.Editor usage where the
   interpreter does not have a named variable for the instance
   and thus does not hold a reference for it. Fails without
   the make_baton/close_baton fix in swigutil_py.c.

* subversion/bindings/swig/svn_repos.i
   (svn_swig_py_make_parse_fns3): Wrap it.
]]]

Regards,
Alexey.