core: Add a function creating an archive-z2 content stream

It is quite similar to the already existing
ostree_raw_file_to_content_stream function, so I factored the common
part to a separate function. The difference is that we cannot report
the size of the resulting stream.

Can be useful for serving a "bare" repository as a faked "archive-z2"
repository.

Closes: #308
Approved by: cgwalters

src/libostree/ostree-core.h

@@ -274,6 +274,15 @@ gboolean ostree_content_file_parse_at (gboolean                compressed,
                                        GCancellable           *cancellable,
                                        GError                **error);
 
+_OSTREE_PUBLIC
+gboolean
+ostree_raw_file_to_archive_z2_stream (GInputStream       *input,
+                                      GFileInfo          *file_info,
+                                      GVariant           *xattrs,
+                                      GInputStream      **out_input,
+                                      GCancellable       *cancellable,
+                                      GError            **error);
+
 _OSTREE_PUBLIC
 gboolean ostree_raw_file_to_content_stream (GInputStream       *input,
                                             GFileInfo          *file_info,