More fixes for reading corrupt ELF files.

More fixes for reading corrupt ELF files.

	PR binutils/15731
	* readelf.c (printable_section_name): New function.
	(printable_section_name_from_index): New function.
	(dump_relocations): Use new function.
	(process_program_headers, get_32bit_elf_symbols,
	(get_64bit_elf_symbols, process_section_headers,
	(process_section_groups, process_relocs, ia64_process_unwind,
	(hppa_process_unwind, get_unwind_section_word, decode_arm_unwind,
	(arm_process_unwind, process_version_sections,
	(process_symbol_table, apply_relocations, get_section_contents,
	(dump_section_as_strings, dump_section_as_bytes,
	(display_debug_section, process_attributes, process_mips_specific,
	(process_mips_specific process_gnu_liblist): Likewise.
	(get_unwind_section_word): Check for a missing symbol table.
	Replace aborts with error messages.
	(arm_process_unwind): Check for a missing string table.
	(process_attributes): Check for an attribute length that is too
	small.
	(process_mips_specific): Check for a corrupt GOT symbol offset.