model: Updated API for pluggable wire format

As of this commit, the selected (default) wire format is controlled via
global variable ndn::WireFormat:

    Config::SetGlobal ("ndn::WireFormat", IntegerValue (ndn::Wire::WIRE_FORMAT_CCNB));

or

    ./waf --run="... --ndn::WireFormat=1

Refs #1008 (http://redmine.named-data.net/issues/1008)
diff --git a/model/ndn-interest.cc b/model/ndn-interest.cc
index 7364701..5d76362 100644
--- a/model/ndn-interest.cc
+++ b/model/ndn-interest.cc
@@ -53,17 +53,7 @@
   , m_payload          (interest.GetPayload ()->Copy ())
   , m_wire             (0)
 {
-}
-
-Interest::Interest (Ptr<const Interest> interest)
-  : m_name             (Create<Name> (interest->GetName ()))
-  , m_scope            (interest->m_scope)
-  , m_interestLifetime (interest->m_interestLifetime)
-  , m_nonce            (interest->m_nonce)
-  , m_nackType         (interest->m_nackType)
-  , m_payload          (interest->GetPayload ()->Copy ())
-  , m_wire             (0)
-{
+  NS_LOG_FUNCTION ("correct copy constructor");
 }
 
 void