Make BytesString.Unsafe internal (which it should have been all along)

csharp/src/Google.Protobuf/ByteString.cs

@@ -50,13 +50,13 @@ namespace Google.Protobuf
         /// <summary>
         /// Unsafe operations that can cause IO Failure and/or other catestrophic side-effects.
         /// </summary>
-        public static class Unsafe
+        internal static class Unsafe
         {
             /// <summary>
             /// Constructs a new ByteString from the given byte array. The array is
             /// *not* copied, and must not be modified after this constructor is called.
             /// </summary>
-            public static ByteString FromBytes(byte[] bytes)
+            internal static ByteString FromBytes(byte[] bytes)
             {
                 return new ByteString(bytes);
             }
@@ -65,7 +65,7 @@ namespace Google.Protobuf
             /// Provides direct, unrestricted access to the bytes contained in this instance.
             /// You must not modify or resize the byte array returned by this method.
             /// </summary>
-            public static byte[] GetBuffer(ByteString bytes)
+            internal static byte[] GetBuffer(ByteString bytes)
             {
                 return bytes.bytes;
             }