setDN() uses a boolean flag instead of string.

This changes the method declaration to accept a boolean instead
of the new DN string. The change happens on the "experimenter"
table ("ldap" column) and not on "password".
SqlAction.java: Remove unused actions, add new.

This removes actions that relied on the "dn" column of the
"password" table and also add surrogate actions that make use
of the new "ldap" column.
PasswordUtil.java: Use updated SQL action.

This simplifies the usage of PasswordUtil and the logic in AdminImpl
and ResetPasswordRequestI.
LdapImpl.java: Update method logic.

This is due to the updates to SQL actions and also the now
available new direct way of checking if a user came from an LDAP
server.