More fixes for memory corruption when readelf processes corrupt files.

More fixes for memory corruption when readelf processes corrupt files.

	PR binutils/17531
	(get_32bit_program_headers): Verify program header entry size
	before reading in the program headers.
	(get_64bit_program_headers): Likewise.
	(get_unwind_section_word): Do nothing if no section was provided.
	Fail if the offset is outside of the section.
	(print_dynamic_symbol): Catch out of range symbol indicies.
	(process_mips_specific): Likewise.
	(process_attributes): Make sure that there is enough space left in
	the section before attempting to read the length of the next
	attribute.