a) A disproportionately high number of Africans in Libya were working for Gaddafi as mercenary soldiers, and in fact many were flown and driven into Libya by Gaddafi during the war, hence the distrust of Africans by the rebels - it's not racism at work here (as your link mentions!).
b) What mass unmarked graves? Quit raving. None have been discovered, and the evidence suggests none ever will, because they don't exist.
c) It is true the rebels have been doing executions on the spot (against the will of the chain of command - the National Transitional Council) OF GADDAFI SOLDIERS instead of taking prisoners. The bodies of a bunch of Gaddafi's extremists have been found this way, some Africans among them, but again, that's kinda because the Africans in question were FIGHTING against the rebels.
4) You didn't even read you're own bloody link. You just wanted to jump on any excuse to have a crack at Barack Obama because you've convinced yourself that he's some sort of Communist devil and thus everything he's associated with is bad. The link rubbishes your post. It even says this "There has been little credible evidence of rebels killing or systematically abusing captives during the six-month conflict."