Ledger acquire fixes/cleanups/logging

* Inbound ledger and SHAMapAddNode cleanup
    * Log acquire stats
    * Fix progress logic
    * Remove ledgers we no longer need to acquire
    * Stash stale state data in our fetch pack, it can still be useful
    * Stash in fetch pack if acquire terminated while job was pending
    * Account for duplicate/invalid nodes in a few cases previously missed
    * Dispatch each InboundLedger once (not per data)
    * Trigger only the "best" peer
    * Don't call tryAdvance on failed acquires

src/ripple_app/misc/Validations.cpp

@@ -122,7 +122,7 @@ private:
         WriteLog (lsDEBUG, Validations) << "Val for " << hash << " from " << signer.humanNodePublic ()
                                         << " added " << (val->isTrusted () ? "trusted/" : "UNtrusted/") << (isCurrent ? "current" : "stale");
 
-        if (val->isTrusted ())
+        if (val->isTrusted () && isCurrent)
             getApp().getLedgerMaster ().checkAccept (hash);
 
         // FIXME: This never forwards untrusted validations