(boat slips at marina leased by REIT are real estate assets in accordance with I.R.C. Sec. 856(c)(4); rental income from boat slips qualified as rents from real estate under I.R.C. Sec. 856(c)(2) and 856(c)(3); such assets count toward requirement that 75 percent of value of REIT's total assets represented by real estate, cash and government securities).