It’s witchcraft! Following the tragic death of Shannen Doherty, actress Rose McGowan revealed she “cannot stop crying” as she opened up about some real black magic swirling on the set of Charmed. RadarOnline.com can reveal that McGowan, 50, shared there were very much “dark forces” at play around the actresses who portrayed witches on the hit ’90s supernatural series. McGowan and Doherty played half-sisters Paige Matthews and Prue Halliwell, respectively. The show also starred Alyssa Milano, 51, and Holly Marie Combs, 50, as Phoebe and Piper Halliwell. McGowan’s comments about dark forces refe…