Switch secondary sort order for version-sorted manifests

To ease human readability of manifests, but without impacting manifest
delta efficiency, use a lexicographic filename secondary sort order when
sorting manifests by version.

Below is an example of how this commit changes the sorted order (the
first column is the version, and the second column is the filename).

 # Before
 10	zyxw
 10	abcd
 20	test2
 20	test1
 20	abba
 20	aaaa
 30	zzyy

 # After
 10	abcd
 10	zyxw
 20	aaaa
 20	abba
 20	test1
 20	test2
 30	zzyy

Signed-off-by: Patrick McCarty <patrick.mccarty@intel.com>

src/manifest.c

@@ -64,7 +64,7 @@ int file_sort_version(gconstpointer a, gconstpointer b)
 		return 1;
 	}
 
-	return strcmp(B->filename, A->filename);
+	return strcmp(A->filename, B->filename);
 }
 
 int file_sort_filename(gconstpointer a, gconstpointer b)