* pt.c (determine_specialization): Just return an error_mark_node.
Also print the decl we want in error messages. If we complain,
return error_mark_node.
(tsubst_friend_function): Set lineno and input_filename so
error messages will be useful.
(instantiate_template): Just return an error_mark_node.
* pt.c (print_template_context): Add new argument.
(maybe_print_template_context): New fn.
(push_tinst_level): Increment tinst_level_tick.
(pop_tinst_level): Likewise.
* errfn.c (cp_thing): Call maybe_print_template_context. Use
xrealloc instead of xmalloc.
* typeck.c (build_unary_op, CONVERT_EXPR): Propagate TREE_CONSTANT.
From-SVN: r19946
