lib/repo: Add ostree_repo_equal() for comparing repos

This will compare their root directory inodes to see if they are the
same repository on disk. A convenience method for the users of the
public API who can’t access OstreeRepo.inode.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

Closes: #1179
Approved by: cgwalters

src/libostree/ostree-repo.h

@@ -123,6 +123,10 @@ GFile *       ostree_repo_get_path (OstreeRepo  *self);
 _OSTREE_PUBLIC
 int           ostree_repo_get_dfd (OstreeRepo  *self);
 
+_OSTREE_PUBLIC
+gboolean      ostree_repo_equal (OstreeRepo *a,
+                                 OstreeRepo *b);
+
 _OSTREE_PUBLIC
 OstreeRepoMode ostree_repo_get_mode (OstreeRepo  *self);