Enable gdb to write to core files on more core file readers.

	Enable gdb to write to core files on more core file readers.
	* libbfd.c (bfd_generic_set_section_contents):  Remove range check
	for section size, it is already done in bfd_set_section_contents
	with bfd_get_section_size_now.
	* aix386-core.c, hppabsd-core.c, hpux-core.c, irix-core.c,
	osf-core.c, ptrace-core.c, trad-core.c (*_set_section_contents):
	Use bfd_generic_set_section_contents instead of bfd_false.