ostree-repo-libarchive.c: major refactor

- Make hardlink handling more generic. The previous strategy worked for
  tar archives, but not for cpio. It now works for both.
- Add support for SEL labeling (through the OstreeRepoCommitModifier)
- Add support for xattr_callback (through the OstreeRepoCommitModifier)
- Add support for filter (through the OstreeRepoCommitModifier)
- Add a use_ostree_convention option

Closes: #275
Approved by: cgwalters

src/libostree/ostree-repo-commit.c

@@ -36,22 +36,6 @@
 #include <sys/xattr.h>
 #include <glib/gprintf.h>
 
-struct OstreeRepoCommitModifier {
-  volatile gint refcount;
-
-  OstreeRepoCommitModifierFlags flags;
-  OstreeRepoCommitFilter filter;
-  gpointer user_data;
-  GDestroyNotify destroy_notify;
-
-  OstreeRepoCommitModifierXattrCallback xattr_callback;
-  GDestroyNotify xattr_destroy;
-  gpointer xattr_user_data;
-
-  OstreeSePolicy *sepolicy;
-  GHashTable *devino_cache;
-};
-
 gboolean
 _ostree_repo_ensure_loose_objdir_at (int             dfd,
                                      const char     *loose_path,