maintainer-scripts/update_web_docs_libstdcxx_svn: add error detection

[Gerald Pfeifer]

On Fri, 5 Apr 2013, Gerald Pfeifer wrote:
> 2013-04-05  Gerald Pfeifer  <gerald@pfeifer.com>
> 
> 	* update_web_docs_libstdcxx_svn: No longer ignore all output from
> 	the actual copy process.
> 	Check the exit code of the actual copy process; diagnose problems.

I committed this now, after it has been active on gcc.gnu.org for a few 
days.  Looks good so far (cf. http://gcc.gnu.org/ml/gccadmin/2013-q2/ ).

Gerald