use errchk in more places.

let errchk exit 0 even if it has reported a BUG.
it echoed BUG and that's all that matters.

R=r
DELTA=143  (1 added, 89 deleted, 53 changed)
OCL=32533
CL=32542

test/fixedbugs/bug146.go

@@ -10,5 +10,5 @@ func main() {
 	type Slice []byte;
 	a := [...]byte{ 0 };
 	b := Slice(&a);		// This should be OK.
-	c := Slice(a);		// ERROR "invalid"
+	c := Slice(a);		// ERROR "invalid|illegal"
 }