set 0.0 and -0.0 to be equal

Reference: /n/sources/patch/applied/fpzero
Date: Tue Apr 16 13:52:02 CES 2013
Signed-off-by: paurea@gmail.com

--- /sys/src/9/port/fpi.c	Tue Apr 16 13:51:31 2013
+++ /sys/src/9/port/fpi.c	Tue Apr 16 13:51:28 2013
@@ -291,6 +291,8 @@
 		return 0;
 	if(IsInfinity(x) && IsInfinity(y))
 		return y->s - x->s;
+	if(IsZero(x) && IsZero(y))
+		return 0;
 	if(x->e == y->e && x->h == y->h && x->l == y->l)
 		return y->s - x->s;
 	if(x->e < y->e