In common.h, remove Ptr.  In interest.h, etc. typedef InterestPtr and ConstInterestPtr, etc.

We will centralize and allow these to be typedef as boost::shared_ptr
or std::shared_ptr.
diff --git a/ndn-cpp/fields/blob.h b/ndn-cpp/fields/blob.h
index 85fd71b..ce0d667 100644
--- a/ndn-cpp/fields/blob.h
+++ b/ndn-cpp/fields/blob.h
@@ -15,9 +15,14 @@
 
 #include <vector>
 #include <cstddef>
+#include <boost/shared_ptr.hpp>
 
 namespace ndn {
 
+class Blob;
+typedef boost::shared_ptr<Blob> BlobPtr;
+typedef boost::shared_ptr<const Blob> ConstBlobPtr;
+
 /**
  * @brief Class representing a general-use binary blob
  */