Extend Gawain to use Blender's built-in shaders

Was already done for immediate mode, but rearranged code to make a clean separation. Cleaned up #includes for code that uses this feature.

Added same for batched rendering.

source/blender/gpu/intern/gpu_batch.c

@@ -0,0 +1,35 @@
+/*
+ * ***** BEGIN GPL LICENSE BLOCK *****
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ *
+ * The Original Code is Copyright (C) 2016 Blender Foundation.
+ * All rights reserved.
+ *
+ * The Original Code is: all of this file.
+ *
+ * Contributor(s): Mike Erwin
+ *
+ * ***** END GPL LICENSE BLOCK *****
+ */
+
+#include "GPU_batch.h"
+#include "gpu_shader_private.h"
+
+void Batch_set_builtin_program(Batch* batch, GPUBuiltinShader shader_id)
+{
+	GPUShader *shader = GPU_shader_get_builtin_shader(shader_id);
+	Batch_set_program(batch, shader->program);
+}