“This isn’t about women’s lib,” crows Kim Fowley (Michael Shannon) in The Runaways, the feature-length debut from renowned music video director Floria Sigismondi. “This is about women’s libidos.” See what he did there? But this quote gets to the paradoxical high-wire act at the heart of this film: lib or libido? Empowerment or exploitation? A film that opens with a close-up of Dakota Fanning’s first drops of menstrual blood hitting the L.A. pavement could go either way.