refs #5010, add assert to toku_txn_manager_pin_live_txn_unlocked verifying that txn being pinned is not read only

git-svn-id: file:///svn/toku/tokudb@45348 c7de825b-a66e-492c-adef-691d508d4ae1

ft/txn_manager.c

@@ -809,6 +809,7 @@ exit:
 // a leafentry.
 void toku_txn_manager_pin_live_txn_unlocked(TXN_MANAGER UU(txn_manager), TOKUTXN txn) {
     assert(txn->state == TOKUTXN_LIVE || txn->state == TOKUTXN_PREPARING);
+    assert(!toku_txn_is_read_only(txn));
     txn->num_pin++;
 }