Don't choose plugin target in binutils/

Don't choose plugin target in binutils/

Instead make bfd_check_format try the plugin target first when the
user hasn't supplied a target.

bfd/
	* format.c (bfd_check_format_matches): Try for a plugin target
	match first.
	* targets.c (bfd_find_target): Don't specially treat "plugin".
binutils/
	* ar.c (plugin_target): Delete.
	(open_inarch): Don't set target of archive elements.
	(replace_members): Use target rather than plugin_target when
	opening replacement or additional files.
	* arsup.c (plugin_target): Delete.  Replace all uses with NULL.
	(ar_open): Don't set element target.
	* bucomm.h (set_plugin_target): Delete.
	* nm.c (plugin_target): Delete.
	(display_archive): Don't set element target.
	(display_file): Alway use target when opening file.
	* objcopy.c (copy_archive): Don't use plugin target for output
	elements.
	* NEWS: Mention stricter target checking.