* lib/prototypes.h, libmisc/salt.c: Add parameters to

* lib/prototypes.h, libmisc/salt.c: Add parameters to
  crypt_make_salt to force the crypt method and number of rounds.
* libmisc/salt.c: Add parameter to SHA_salt_rounds to force the
  number of rounds.
* libmisc/salt.c, lib/getdef.c: ENCRYPT_METHOD and MD5_CRYPT_ENAB
  are needed also when USE_PAM (e.g. for chpasswd).
* src/newusers.c, src/gpasswd.c: Use the new crypt_make_salt prototype.
* src/chpasswd.c, src/chgpasswd.c: Add option -c, --crypt-method
  and -s, --sha-rounds to specify the crypt method and number of
  rounds in case of one of the SHA methods. The new prototype of
  crypt_make_salt simplifies the handling of -m, --md5.