fix some more struct/class confusions

apps/dsm/DSMSession.h

@@ -92,7 +92,7 @@ typedef map<string, string> VarMapT;
 typedef map<string, AmArg>  AVarMapT;
 
 class DSMDisposable;
-class AmPlaylistItem;
+struct AmPlaylistItem;
 
 class DSMSession {
 

apps/registrar_client/SIPRegistrarClient.h

@@ -155,7 +155,7 @@ class SIPRegistration : public AmSipDialogEventHandler,
   const string& getEventSink() { return sess_link; }
 };
 
-class SIPNewRegistrationEvent;
+struct SIPNewRegistrationEvent;
 class SIPRemoveRegistrationEvent;
 
 class SIPRegistrarClient  : public AmThread,

apps/voicemail/AmMail.h

@@ -59,7 +59,7 @@ struct Attachement
 
 typedef std::vector<Attachement> Attachements;
 
-class AmMail;
+struct AmMail;
 
 /**
  * Function pointer to be called after mail processing.

apps/voicemail/EmailTemplate.h

@@ -32,7 +32,7 @@
 #include <string>
 using std::string;
 
-class AmMail;
+struct AmMail;
 
 typedef std::map<std::string,std::string> EmailTmplDict;