Access Journal::Stream using member functions (RIPD-1087):

Replace Journal public data members with member function accessors
in order to make Journal lighter weight.  The change makes a
Journal cheaper to pass by value.

Also add missing stream checks (e.g., calls to JLOG) to avoid
text processing that ultimately will not be stored in the log.

src/ripple/app/ledger/impl/InboundLedgers.cpp

@@ -159,7 +159,7 @@ public:
     {
         protocol::TMLedgerData& packet = *packet_ptr;
 
-        JLOG (j_.trace)
+        JLOG (j_.trace())
             << "Got data (" << packet.nodes ().size ()
             << ") for acquiring ledger: " << hash;
 
@@ -167,7 +167,7 @@ public:
 
         if (!ledger)
         {
-            JLOG (j_.trace)
+            JLOG (j_.trace())
                 << "Got data for ledger we're no longer acquiring";
 
             // If it's state node data, stash it because it still might be
@@ -401,7 +401,7 @@ public:
 
         }
 
-        JLOG (j_.debug) <<
+        JLOG (j_.debug()) <<
             "Swept " << stuffToSweep.size () <<
             " out of " << total << " inbound ledgers.";
     }