pack: packfile_free -> git_packfile_free and use it in the indexers

It turns out the indexers have been ignoring the pack's free function
and leaking data. Plug that.

src/indexer.c

@@ -747,7 +747,7 @@ void git_indexer_stream_free(git_indexer_stream *idx)
 	git_vector_foreach(&idx->deltas, i, delta)
 		git__free(delta);
 	git_vector_free(&idx->deltas);
-	git__free(idx->pack);
+	git_packfile_free(idx->pack);
 	git__free(idx);
 }
 
@@ -1059,7 +1059,7 @@ void git_indexer_free(git_indexer *idx)
 	git_vector_foreach(&idx->pack->cache, i, pe)
 		git__free(pe);
 	git_vector_free(&idx->pack->cache);
-	git__free(idx->pack);
+	git_packfile_free(idx->pack);
 	git__free(idx);
 }
 

src/odb_pack.c

@@ -538,7 +538,7 @@ static void pack_backend__free(git_odb_backend *_backend)
 
 	for (i = 0; i < backend->packs.length; ++i) {
 		struct git_pack_file *p = git_vector_get(&backend->packs, i);
-		packfile_free(p);
+		git_packfile_free(p);
 	}
 
 	git_vector_free(&backend->packs);

src/pack.c

@@ -794,7 +794,7 @@ static struct git_pack_file *packfile_alloc(size_t extra)
 }
 
 
-void packfile_free(struct git_pack_file *p)
+void git_packfile_free(struct git_pack_file *p)
 {
 	assert(p);