“ SPECIAL RULE IN CASE OF DISCRETION TO IDENTIFY BENEFICIARIES- For purposes of paragraph (1) (A) , if any person has the discretion (by authority given in the trust agreement, by power of appointment, or otherwise) of making a distribution from the trust to, or for the benefit of, any person, such trust shall be treated as having a beneficiary who is a United States person unless-- ` (A) the terms of the trust specifically identify the class of persons to whom such distributions may be made, and ` (B) none of those persons are United States persons during the taxable year.'. ”