bloom: annotate filters with hash version

In subsequent commits, we will want to load existing Bloom filters out
of a commit-graph, even when the hash version they were computed with
does not match the value of `commitGraph.changedPathVersion`.

In order to differentiate between the two, add a "version" field to each
Bloom filter.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

bloom.h

@@ -53,6 +53,7 @@ struct bloom_filter_settings {
 struct bloom_filter {
 	unsigned char *data;
 	size_t len;
+	int version;
 };
 
 /*