Set prefix in snapshots when using dwimmery

This patch sets the directory prefix in archives to be the filename,
excluding the suffix (.tar.gz, .tar.bz2 etc).

The patch also removes the prefix parameter in cgit_print_snapshot()
as the prefix might differ.

Signed-off-by: Lars Hjemli <hjemli@gmail.com>

cmd.c

@@ -104,8 +104,7 @@ static void refs_fn(struct cgit_context *ctx)
 
 static void snapshot_fn(struct cgit_context *ctx)
 {
-	cgit_print_snapshot(ctx->qry.head, ctx->qry.sha1,
-			    cgit_repobasename(ctx->repo->url), ctx->qry.path,
+	cgit_print_snapshot(ctx->qry.head, ctx->qry.sha1, ctx->qry.path,
 			    ctx->repo->snapshots, ctx->qry.nohead);
 }