THE UDF05 FOLLOW-UP OF THE HUBBLE ULTRA DEEP FIELD. II. CONSTRAINTS ON REIONIZATION FROM Z-DROPOUT GALAXIESMostly based on data obtained with the Hubble Space Telescope operated by Association of Universities for Research in Astronomy (AURA), Inc. for NASA under contract NAS5-26555. Partly based on data from the Spitzer Space Telescope operated by Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407.