readelf section reading

readelf section reading

This is a followup to git commit 8ff66993e0b5, a patch aimed at
segfaults found invoking readelf multiple times with fuzzed objects.
In that patch I added code to clear more stashed data early in
process_section_headers, along with any stashed section headers.  This
patch instead relies on clearing out the stash at the end of
process_object, making sure that process_object doesn't exit early.

The patch also introduces some new wrapper functions.

	* readelf.c (GET_ELF_SYMBOLS): Delete.  Replace with..
	(get_elf_symbols): ..this new function throughout.
	(get_32bit_section_headers): Don't free section_headers.
	(get_64bit_section_headers): Likewise.
	(get_section_headers): New function, use throughout in place of
	32bit and 64bit variants.
	(get_dynamic_section): Similarly.
	(process_section_headers): Don't free filedata memory here.
	(get_file_header): Don't get section headers here..
	(process_object): ..Read them here instead.  Don't exit without
	freeing filedata memory.