From Rajiv Joseph’s Dakar 2000 , at City Center. Photo: Matthew Murphy For a tense, 90-minute two-hander, Dakar 2000 has an awful lot on its mind. The play is a thriller about a Peace Corps volunteer caught up in a State Department official’s schemes in Senegal, an anxiety piece about people facing what they think will be the Y2K apocalypse, an exaggerated memoir that comes with lived-in detail, and a meditation on American interventionism abroad that strains to wink at current events. From the