Compiling with gcc 4.9 sometimes requires cstddef

It's the generated swig code that is missing cstddef.  Added some
includes to get cstdef in the swig code.

refs #212

libexec/trick/convert_swig

@@ -322,6 +322,11 @@ sub process_file() {
         print OUT "#include \"trick/swig/trick_swig.i\"\n\n" ;
 
         print OUT "
+\%insert(\"begin\") \%{
+#include <Python.h>
+#include <cstddef>
+\%}
+
 \%{
 #include \"$f\"
 \%}\n" ;

libexec/trick/pm/s_source.pm

@@ -49,6 +49,7 @@ PURPOSE:
 #include <new>
 #include <iostream>
 #include <stdlib.h>
+#include <cstddef>
 
 #include \"trick/attributes.h\"
 #include \"trick/populate_attribute_maps.hh\"

trick_source/trick_swig/sim_services.i

@@ -1,6 +1,10 @@
 
 %module sim_services
 
+%{
+#include <cstddef>
+%}
+
 #include "trick/swig/trick_swig.i"
 #include "trick/swig/units_attach.i"
 #include "trick/swig/extra_functions.i"