widl: Use is_string_type for detecting strings in write_typeformatstring_var to make it consistent with write_remoting_arg.

Fix the is_string_type function used for detecting strings by only 
examining aliases instead of both aliases and pointers. This is due to 
the requirement that pointers to strings be handled as pointers and so 
not detected as strings.

shell32: Support getting the shell folder path for users other than the current user and the default user.