re PR c++/7586 (Incorrect handling of attributes in template codes)

        PR c++/7586
        * pt.c (tsubst): Handle typedefs by looking for the specialization.
        (retrieve_specialization): Only tagged types use
        DECL_TEMPLATE_INSTANTIATIONS.
        (instantiate_class_template): Push nested classes too.
        (tsubst_decl) [TYPE_DECL]: Only check for canonical decl for
        tagged types.
        * cp-tree.h (MAYBE_TAGGED_TYPE_P): New macro.
        * init.c (is_aggr_type): Remove redundant tests.
        * class.c (push_nested_class): Use CLASS_TYPE_P.

From-SVN: r128621