am 95736e8c: Merge changes from topic \'file_contexts.bin\'

* commit '95736e8c6bd7a1e1717cf8abe10f6af910b7e429':
  libselinux: support context validation on file_contexts.bin
  libselinux: test for file_contexts.bin format
  libselinux: add selabel_cmp interface and label_file backend
  libselinux: switch to file_contexts.bin
  libselinux: support specifying file_contexts.bin file path
  libselinux: support file_contexts.bin without file_contexts