In light of the recent forum discussions about Ed Lansdale's relationship with Allen Dulles, and his "black ops" success in establishing the Magsaysay regime in the Philippines and the Diem regime in South Vietnam, should we review Col. L. Fletcher Prouty's "Lansdale Hypothesis" about the JFK assassination op in more detail?         Mr. X's theories about the JFK assassination were an important scene in Oliver Stone's JFK film, and Mr. X (Prouty) outlined them in some detail in his March 6,