(Stringify) enum-to-string functions are in the "rose" namespace

* The automatically-generated functions for converting enum constants
  into strings now live in the "rose" namespace.

* The perl script that generates enum stringification functions
  ignores the "rose" namespace so that "rose" is not part of
  the name of the generated functions.

Example:

  namespace rose {
      class Class {
          enum ValueType { CONSTANT, VARIABLE, OTHER };

Causes generation of:

  namespace rose {
      std::string stringifyClassValueType(Class::ValueType, ...);
Added "using namespace rose" where necessary.

The files in this commit use features from the "rose" namespace
but are not themselves in the "rose" namespace yet.  Eventually
these files will be incorporated into the "rose" namespace and
the "using namespace rose" can go away.