[Patch] trivial fix for sin(const complex<_Tp>& __z)

[Benjamin Kosnik]

> 2004-06-09  Jan van Dijk  <jan@etpmod.phys.tue.nl>
>+ 	* include/std/std_complex.h (sin(const complex<_Tp>& __z)): Make
>+ 	this function return a value.

This is in, thanks.

-benjamin