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
diff --git a/test/fixedbugs/bug074.go b/test/fixedbugs/bug074.go
index d9865c5..7b6d14e 100644
--- a/test/fixedbugs/bug074.go
+++ b/test/fixedbugs/bug074.go
@@ -7,6 +7,6 @@
 package main
 
 func main() {
-	x := string{'a', 'b', '\n'};
+	x := string{'a', 'b', '\n'};	// ERROR "composite"
 	print(x);
 }