Qickhack to fix sosy-lab/java-smt#310. This will make all the threads…

… use the same NodeManager. As a result Solver instances can move between threads. However, no two solver threads may ever run at the same time.

src/expr/node_manager_template.cpp

@@ -129,7 +129,7 @@ NodeManager::NodeManager()
 
 NodeManager* NodeManager::currentNM()
 {
-  thread_local static NodeManager nm;
+  static NodeManager nm;
   return &nm;
 }