deltas: Link to liblzma, add internal API to use it

For future static deltas work, we'll be linking to liblzma.  Since
it's fairly widespread, let's just make it a hard dependency.

src/libostree/ostree-lzma-common.h

@@ -0,0 +1,28 @@
+/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*-
+ *
+ * Copyright (C) 2014 Colin Walters <walters@redhat.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General
+ * Public License along with this library; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <gio/gio.h>
+#include <lzma.h>
+
+G_BEGIN_DECLS
+
+GConverterResult _ostree_lzma_return (lzma_ret value, GError **error);
+
+G_END_DECLS