Add an archive-z repository mode

This is where loose content objects are stored as one compressed file,
instead of the two separate ones for regular archive mode.  This mode
would be suitable for HTTP servers, beause only one HTTP request is
necessary, and the result would be compressed.

src/libostree/ostree-core.h

@@ -127,7 +127,8 @@ void ostree_object_from_string (const char *str,
                                 OstreeObjectType *out_objtype);
 
 char *ostree_get_relative_object_path (const char        *checksum,
-                                       OstreeObjectType   type);
+                                       OstreeObjectType   type,
+                                       gboolean           compressed);
 
 char *ostree_get_relative_archive_content_path (const char        *checksum);
 
@@ -169,6 +170,12 @@ ostree_content_stream_parse (GInputStream           *input,
                              GCancellable           *cancellable,
                              GError                **error);
 
+gboolean ostree_zlib_content_stream_open (GInputStream           *input,
+                                          guint64                *out_len,
+                                          GInputStream          **out_uncompressed,
+                                          GCancellable           *cancellable,
+                                          GError                **error);
+
 gboolean ostree_content_file_parse (GFile                  *content_path,
                                     gboolean                trusted,
                                     GInputStream          **out_input,