Add arc management header to the tests

Author: Wilhelmina Drengwitz

peertalk-tests/PTProtocolTests.h

@@ -1,6 +1,7 @@
 #import <XCTest/XCTest.h>
 #include <dispatch/dispatch.h>
 #import "PTProtocol.h"
+#import "PTPrivate.h"
 
 @interface PTProtocolTests : XCTestCase {
   dispatch_fd_t socket_[2];