Fix "go get" failure

Move the statusTxtContent to fix this confusing error
when running `go get github.com/rfjakob/gocryptfs/...`:

  $ go get github.com/rfjakob/gocryptfs/...
  # github.com/rfjakob/gocryptfs/tests/example_filesystems
  tests/example_filesystems/example_test_helpers.go:22:16: undefined: statusTxtContent
  tests/example_filesystems/example_test_helpers.go:75:16: undefined: statusTxtContent

2 files changed, 2 insertions, 2 deletions

diff --git a/tests/example_filesystems/example_filesystems_test.go b/tests/example_filesystems/example_filesystems_test.go
index b1e0fda..08cd958 100644
--- a/tests/example_filesystems/example_filesystems_test.go
+++ b/tests/example_filesystems/example_filesystems_test.go
@@ -18,8 +18,6 @@ import (
 	"github.com/rfjakob/gocryptfs/tests/test_helpers"
 )
 
-const statusTxtContent = "It works!\n"
-
 var opensslOpt string
 
 // tmpFsPath contains a private writeable copy of the example_filesystems
diff --git a/tests/example_filesystems/example_test_helpers.go b/tests/example_filesystems/example_test_helpers.go
index 672b668..e39f8d6 100644
--- a/tests/example_filesystems/example_test_helpers.go
+++ b/tests/example_filesystems/example_test_helpers.go
@@ -9,6 +9,8 @@ import (
 	"github.com/rfjakob/gocryptfs/tests/test_helpers"
 )
 
+const statusTxtContent = "It works!\n"
+
 // checkExampleFS - verify that "dir" contains the expected test files
 func checkExampleFS(t *testing.T, dir string, rw bool) {
 	// Read regular file