net/http/cgi: maybe improve darwin test reliability

Use a 17 MB payload instead of a 1 MB payload, since
OS X can apparently buffer up to 16 MB in its pipes.

Fixes #4958 maybe

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/7453049

src/pkg/net/http/cgi/host_test.go

@@ -301,9 +301,6 @@ func TestCopyError(t *testing.T) {
 	if runtime.GOOS == "windows" {
 		t.Skipf("skipping test on %q", runtime.GOOS)
 	}
-	if runtime.GOOS == "darwin" {
-		t.Skipf("issue 4958 - skipping test on darwin")
-	}
 	h := &Handler{
 		Path: "testdata/test.cgi",
 		Root: "/test.cgi",

src/pkg/net/http/cgi/testdata/test.cgi

@@ -24,7 +24,8 @@ print "X-Test-Header: X-Test-Value\r\n";
 print "\r\n";
 
 if ($params->{"bigresponse"}) {
-    for (1..1024) {
+    # 17 MB, for OS X: golang.org/issue/4958
+    for (1..(17 * 1024)) {
         print "A" x 1024, "\r\n";
     }
     exit 0;