Passed field name as prefix for nested structs

This pull request should fix google#232.
Pass field name instead of struct name as nameprefix for nested structures. Continuously concatenate nameprefix arguments to support deeper nested structures.

src/idl_gen_general.cpp

@@ -450,7 +450,7 @@ static void GenStructArgs(const LanguageParameters &lang,
       // don't clash, and to make it obvious these arguments are constructing
       // a nested struct, prefix the name with the struct name.
       GenStructArgs(lang, *field.value.type.struct_def, code_ptr,
-                    (field.value.type.struct_def->name + "_").c_str());
+                    (nameprefix + (field.name + "_")).c_str());
     } else {
       code += ", ";
       code += GenTypeForUser(lang,