Fix a potential buffer overrun qwhen writing out PE aux entries.

	* peXXigen.c (_bfd_XXi_swap_aux_out): Avoid potential buffer
	overrun by using sizeof of the destination x_fname field as the
	limit for a memcpy.

	* coff/internal.h (struct internal_auxent): Fix a couple of typos
	in comment describing the x_fname field.