"Project Runway" is returning with a "Project Runway: All-Star Challenge."It will be a two-hour special set to air before the shows season 6 premiere on Aug. 20. Designer Korto Momolu of "Project Runway's" season 5 and Mychael Knight of season 3 will return with other past contestants. Both contestants will compete for $100,000 prize against Daniel Vosovic and Santino Rice of season 2, Jeffrey Sebelia and Uli Herzner of season 3, and Chris March and Sweet P of season 4.