Use udunits package for units conversions.

FieldDescription.cpp is missing and include for stack.  Strange it compiles
on most platforms.

refs #231

trick_source/codegen/Interface_Code_Gen/FieldDescription.cpp

@@ -3,6 +3,7 @@
 #include <algorithm>
 #include <sstream>
 #include <set>
+#include <stack>
 
 #include <libgen.h>
 #include <regex.h>