readelf and objdump help

Splitting up help strings makes it more likely that at least some of
the help translation survives adding new options.

	* readelf.c (parse_args): Call dwarf_select_sections_all on
	--debug-dump without optarg.
	(usage): Associate -w and --debug-dump options closely.
	Split up help message.  Remove extraneous blank lines around
	ctf help.
	* objdump.c (usage): Similarly.