crypto: add import comments.

Change-Id: I33240faf1b8620d0cd600de661928d8e422ebdbc
Reviewed-on: https://go-review.googlesource.com/1235
Reviewed-by: Andrew Gerrand <adg@golang.org>

ssh/testdata/doc.go

@@ -5,4 +5,4 @@
 // This package contains test data shared between the various subpackages of
 // the code.google.com/p/go.crypto/ssh package. Under no circumstance should
 // this data be used for production code.
-package testdata
+package testdata // import "golang.org/x/crypto/ssh/testdata"