launch_daemon: added support for arbitrary ports.

* Dropped "create_port" -- this is now the default for services.
* Additionally (or alternatively, if you use the "legacy" mode), you can
  now create named ports, and specify their capacity.
* Added convenience methods to BLaunchRoster that automatically use the
  signature of the current be_app.

headers/private/app/LaunchRoster.h

@@ -16,9 +16,11 @@ public:
 
 			status_t			InitCheck() const;
 
+			status_t			GetData(BMessage& data);
 			status_t			GetData(const char* signature, BMessage& data);
+			port_id				GetPort(const char* name = NULL);
 			port_id				GetPort(const char* signature,
-									const char* name = NULL);
+									const char* name);
 
 private:
 			void				_InitMessenger();