* section.c (bfd_abs_section): Make const.

	* section.c (bfd_abs_section): Make const.
	(bfd_abs_section_ptr, bfd_is_abs_section): Define.
	(bfd_und_section): Make const.
	(bfd_und_section_ptr, bfd_is_und_section): Define.
	(bfd_com_section): Make const.
	(bfd_com_section_ptr): Define.
	(bfd_ind_section): Make const.
	(bfd_ind_section_ptr, bfd_is_ind_section): Define.
	(bfd_abs_symbol, bfd_com_symbol): Make const.
	(bfd_und_symbol, bfd_ind_symbol): Likewise.
	(global_syms): Cast initialization of section field.
	(STD_SECTION): Define as const, and cast initializations.
	* bfd-in2.h: Rebuilt.
	* Many files: Change uses of bfd_abs_section, etc., to use
	bfd_abs_section_ptr or bfd_is_abs_section, etc.