* ropeimpl.h: Check __STL_PTHREADS instead of _PTHREADS.
	* stl_alloc.h: Ditto.
	* stl_config.h: Ditto.
	* stl_rope.h: Ditto.
	* stl_config.h: include <_G_config.h> if __GNUG__ is defined.
	(__STL_PTHREADS): Defined if _PTHREADS is defined or
	__GLIBC__ >= 2.

From-SVN: r18138