obstack-zprintf: New module. * lib/stdio.in.h (obstack_zprintf, obstack_vzprintf): New declarations. (obstack_printf, obstack_vprintf): Tweak comment. * lib/obstack_printf.c: Parameterize. (RESULT_TYPE, OBSTACK_PRINTF, OBSTACK_VPRINTF): New macros. * lib/obstack_zprintf.c: New file. * m4/stdio_h.m4 (gl_STDIO_H_REQUIRE_DEFAULTS): Initialize GNULIB_OBSTACK_ZPRINTF. * modules/stdio (Makefile.am): Substitute GNULIB_OBSTACK_ZPRINTF. * modules/obstack-zprintf: New file.