core: Make OstreeRepoFile "public"

* "ls" used it
* It's not like our internal API is 100% stable anyways
* The _ is ugly

src/libostree/ostree.h

@@ -26,5 +26,6 @@
 #include <ostree-repo.h>
 #include <ostree-checkout.h>
 #include <ostree-mutable-tree.h>
+#include <ostree-repo-file.h>
 
 #endif