stdopen: modernize and simplify * lib/stdopen.c: Update copyright date Do not include sys/types.h; no longer needed these days. (stdopen): Use C99-style decl in loop. Return int errno value, rather than just a bool. Do not worry about fd mismatches, since the caller cares only if 0, 1, 2 are occupied. * lib/stdopen.h: No need to include <stdbool.h>. * m4/stdopen.m4: Remove. * modules/stdopen: New file.