Add files to Makefile.am to fix dist targets

Makefile.am

@@ -100,6 +100,7 @@ csharp_EXTRA_DIST=                                                           \
   csharp/src/Google.Protobuf.Test/JsonParserTest.cs                          \
   csharp/src/Google.Protobuf.Test/JsonTokenizerTest.cs                       \
   csharp/src/Google.Protobuf.Test/Reflection/CustomOptionsTest.cs            \
+  csharp/src/Google.Protobuf.Test/Reflection/DescriptorDeclarationTest.cs    \
   csharp/src/Google.Protobuf.Test/Reflection/DescriptorsTest.cs              \
   csharp/src/Google.Protobuf.Test/Reflection/FieldAccessTest.cs              \
   csharp/src/Google.Protobuf.Test/Reflection/TypeRegistryTest.cs             \
@@ -122,6 +123,7 @@ csharp_EXTRA_DIST=                                                           \
   csharp/src/Google.Protobuf.Test/WellKnownTypes/TimestampTest.cs            \
   csharp/src/Google.Protobuf.Test/WellKnownTypes/WrappersTest.cs             \
   csharp/src/Google.Protobuf.Test/UnknownFieldSetTest.cs                     \
+  csharp/src/Google.Protobuf.Test/testprotos.pb                              \
   csharp/src/Google.Protobuf.sln                                             \
   csharp/src/Google.Protobuf/ByteArray.cs                                    \
   csharp/src/Google.Protobuf/ByteString.cs                                   \
@@ -157,6 +159,7 @@ csharp_EXTRA_DIST=                                                           \
   csharp/src/Google.Protobuf/Reflection/CustomOptions.cs                     \
   csharp/src/Google.Protobuf/Reflection/Descriptor.cs                        \
   csharp/src/Google.Protobuf/Reflection/DescriptorBase.cs                    \
+  csharp/src/Google.Protobuf/Reflection/DescriptorDeclaration.cs             \
   csharp/src/Google.Protobuf/Reflection/DescriptorPool.cs                    \
   csharp/src/Google.Protobuf/Reflection/DescriptorUtil.cs                    \
   csharp/src/Google.Protobuf/Reflection/DescriptorValidationException.cs     \