Added explicit #include <cstddef> to try to meet stlport and others needing errno definition.

[SVN r66886]

example/error_handling_example.cpp

@@ -63,6 +63,9 @@ We'll begin our sample program with the needed includes:
 #include <stdexcept>
    using std::exception;
 
+#include <cstddef>
+   // using ::errno
+
 /*`
 Next we'll define the program's main() to call the student's t
 distribution with an invalid degrees of freedom parameter,