Fix roundtripping of binary data, add unit test

plist-cil.test/BinaryPropertyListWriterTests.cs

@@ -0,0 +1,25 @@
+using Claunia.PropertyList;
+using System.IO;
+using Xunit;
+
+namespace plistcil.test
+{
+    public class BinaryPropertyListWriterTests
+    {
+        [Fact]
+        public void RoundtripTest()
+        {
+            byte[] data = File.ReadAllBytes("test-files/plist.bin");
+            NSObject root = PropertyListParser.Parse(data);
+
+            using (MemoryStream actualOutput = new MemoryStream())
+            using (Stream expectedOutput = File.OpenRead("test-files/plist.bin"))
+            using (ValidatingStream validatingStream = new ValidatingStream(actualOutput, expectedOutput))
+            {
+                BinaryPropertyListWriter writer = new BinaryPropertyListWriter(validatingStream);
+                writer.ReuseObjectIds = false;
+                writer.Write(root);
+            }
+        }
+    }
+}