Refactor and test Variable Server.

- Split VariableServerThread into VariableServerSession and VariableReference classes
- Use C++ streams for data handling
- Unit tests

trick_source/sim_services/VariableServer/VariableServerSession_freeze_init.cpp

@@ -0,0 +1,16 @@
+
+#include <iostream>
+#include <string.h>
+
+#include "trick/VariableServerSession.hh"
+#include "trick/TrickConstant.hh"
+
+int Trick::VariableServerSession::freeze_init() {
+    if ( enabled && copy_mode == VS_COPY_SCHEDULED) {
+        freeze_next_tics = cycle_tics ;
+    } else {
+        freeze_next_tics = TRICK_MAX_LONG_LONG ;
+    }
+    return 0 ;
+}
+