(_ufc_setup_salt_r): Return bool.
* crypt/crypt-entry.c: Include errno.h.
(__crypt_r): Return NULL with EINVAL for bad salt.
* crypt/crypt_util.c (bad_for_salt): New.
(_ufc_setup_salt_r): Check that salt is long enough and within
the specified alphabet.
* crypt/badsalttest.c: New file.
* crypt/Makefile (tests): Add it.
($(objpfx)badsalttest): New.