* rs6000-core.c: Support 64-bit core files, support pre-4.3 core

	* rs6000-core.c: Support 64-bit core files, support pre-4.3 core
	files on AIX 4.3.
	(read_hdr): New function.
	(rs6000coff_core_p): Store mstsave or __context64 struct instead
	of trying to extract individual registers.  Set abfd->arch_info
	to match the architecture that created the core file.
	(rs6000coff_get_section_contents): Delete.
	* xcoff-target.h (rs6000coff_get_section_contents): Delete.