* Use <replaceable> for the values set by

* Use <replaceable> for the values set by
  users. (was sometimes <emphasis remap='I'>)
* Use <option> vor the variable names. This
  makes the manpage much more readable.
* (ENCRYPT_METHOD, MD5_CRYPT_ENAB,
  SHA_CRYPT_MIN_ROUNDS, SHA_CRYPT_MAX_ROUNDS): Mention that command
  line option may supersede the system setting.
* Document the variables used by chpasswd
  and chgpasswd.