Errata:
A format string vulnerability exists in the pw_error(3) function. This
manifests itself as a security hole in the chpass utility.
Fix:
warnx?/errx? paranoia (use "%s" not a bare string unless it is a
constant).  These are not security holes but it is worth fixing
them anyway both for robustness and so folks looking for examples
in the tree are not misled into doing something potentially dangerous.
Furthermore, it is a bad idea to assume that pathnames will not
include '%' in them and that error routines don't return strings
with '%' in them (especially in light of the possibility of locales).