[PATCH] Add platform information to user agent string

Hi,

I think it will be useful to add client platform information to user
agent string, to use it Apache HTTP Server configuration or Subversion
hooks. Within my patch applied user agent will be like this:
SVN/1.8.0 (Windows) serf/1.1.1 TortoiseSVN/1.8.0
SVN/1.8.0 (Macintosh) serf/1.1.1
SVN/1.8.0 (FreeBSD) serf/1.1.1

[[[
* subversion/libsvn_ra_serf/ra_serf.h
  (USER_AGENT_PLATFORM): New.
  (USER_AGENT): Add platform information.
]]]

Any objections?

I've tested it only on Windows, so more testing would be useful.

[1] http://sourceforge.net/p/predef/wiki/OperatingSystems/

-- 
Ivan Zhakov