strings: Remove cmStdString references

Casts from std::string -> cmStdString were high on the list of things
taking up time. Avoid such implicit casts across function calls by just
using std::string everywhere.

The comment that the symbol name is too long is no longer relevant since
modern debuggers alias the templates anyways and the size is a
non-issue since the underlying methods are generated since it's
inherited.

Source/cmGlobalVisualStudio6Generator.h

@@ -103,7 +103,7 @@ private:
                     cmTarget const& t);
   void WriteExternalProject(std::ostream& fout,
                             const std::string& name, const char* path,
-                            const std::set<cmStdString>& dependencies);
+                            const std::set<std::string>& dependencies);
   void WriteDSWFooter(std::ostream& fout);
   virtual std::string WriteUtilityDepend(cmTarget const* target);
   std::string MSDevCommand;