Make Python file-like objects passable to svn_stream_t* input parameters

Patch by Brandon Ehle at
http://www.contactor.se/~dast/svn/archive-2003-07/1570.shtml
Log message: 
* Add a typemap for svn_client_prompt_t

* Add a typemap for log_message_receiver_t

* Add a python wrapper ||svn_stream_from_pyio around svn_stream_t for
 passing python objects that have read & write methods

* Supply a return type mapping for type svn_stream_t **

* Fix a comment in svn_client.i

http://www.contactor.se/~dast/svn/archive-2003-07/1570.shtml

Original issue reported by sander