Standard LDAP Password Encryption

This patch adds more flexibility to the password encryption feature.

The old mechanism would only write cleartext or MD5 password hashes back to LDAP wherein this new method handles many more encryption types like salted hashes and SHA. It does check to see if these additional encryption types are supported by PHP at configuration time.

The patch includes a database update (currently number 6003) that renames the "encrypted" column to "enc_type" to better reflect the data stored. Also, the old values of the column were not remapped to keep disruption at a minimum ( '0' = clear, '1' = MD5).

Tested with D6.14 and OpenLDAP.