std_sstream.h (basic_stringbuf<>::setbuf): Simply clear the internal _M_string, adjust _M_sync call.

2006-02-19  Paolo Carlini  <pcarlini@suse.de>

	* include/std/std_sstream.h (basic_stringbuf<>::setbuf): Simply
	clear the internal _M_string, adjust _M_sync call.
	* include/bits/sstream.tcc (basic_stringbuf<>::_M_sync): Adjust
	consistently for calls from setbuf.

From-SVN: r111274