At the beginning of Rajiv Joseph’s new play, “Dakar 2000,” a guy who calls himself Boubs tells us the story we’re about to see is “almost entirely true.” Boubs, an abbreviation for Boubacar — the character is half Indian — allows that names and some places have been changed, and that some of “the boring parts” have been “snipped away. Some other stuff has been added to make it … theoretically more interesting.”