go/doc: avoid the name 'a.out' in the testdata

R=golang-dev, gri, r
CC=golang-dev
https://golang.org/cl/5561047

src/pkg/go/doc/testdata/a0.go

@@ -3,6 +3,6 @@
 // license that can be found in the LICENSE file.
 
 // comment 0
-package a
+package alpha
 
 //BUG(uid): bug0

src/pkg/go/doc/testdata/a1.go

@@ -3,6 +3,6 @@
 // license that can be found in the LICENSE file.
 
 // comment 1
-package a
+package alpha
 
 //BUG(uid): bug1

src/pkg/go/doc/testdata/a.out → src/pkg/go/doc/testdata/alpha.out

 // comment 0  comment 1 
-PACKAGE a
+PACKAGE alpha
 
 IMPORTPATH
-	testdata/a
+	testdata/alpha
 
 FILENAMES
 	testdata/a0.go