[sledge] Rename some unary predicates with is_-prefixes
[sledge] Rename some unary predicates with is_-prefixes

Reviewed By: jvillard

Differential Revision: D24934115

fbshipit-source-id: 327ae1979

facebook/infer,jvillard/infer,jvillard/infer,jvillard/infer,facebook/infer,jvillard/infer,facebook/infer,jvillard/infer,facebook/infer,facebook/infer,facebook/infer,facebook/infer,jvillard/infer,jvillard/infer