[OPENGL32][MESA] Downgrade Mesa library to version 2.6

With this commit, we now use a forked version of MESA which only supports OpenGL 1.1, like the windows implementation does.
It exposes :
  - The same pixel formats
  - The same set of extensions
  - Nothing more
All of this without taking 10% of your build time.
If you need a more modern option, look at the MESA package from Rapps, which is (and must be) maintained outside of this code tree.
CORE-7499

dll/opengl/mesa/texobj.h

@@ -0,0 +1,88 @@
+/* $Id: texobj.h,v 1.3 1997/09/23 00:58:15 brianp Exp $ */
+
+/*
+ * Mesa 3-D graphics library
+ * Version:  2.3
+ * Copyright (C) 1995-1996  Brian Paul
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Library 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
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ * License along with this library; if not, write to the Free
+ * Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+
+/*
+ * $Log: texobj.h,v $
+ * Revision 1.3  1997/09/23 00:58:15  brianp
+ * now using hash table for texture objects
+ *
+ * Revision 1.2  1997/04/28 23:37:34  brianp
+ * added gl_test_texture_object_completeness()
+ *
+ * Revision 1.1  1996/09/13 01:38:16  brianp
+ * Initial revision
+ *
+ */
+
+
+#ifndef TEXTOBJ_H
+#define TEXTOBJ_H
+
+
+#include "types.h"
+
+
+/*
+ * Internal functions
+ */
+
+extern struct gl_texture_object *
+gl_alloc_texture_object( struct gl_shared_state *shared, GLuint name,
+                         GLuint dimensions );
+
+
+extern void gl_free_texture_object( struct gl_shared_state *shared,
+                                    struct gl_texture_object *t );
+
+
+extern void gl_test_texture_object_completeness( struct gl_texture_object *t );
+
+
+/*
+ * API functions
+ */
+
+extern void gl_GenTextures( GLcontext *ctx, GLsizei n, GLuint *textures );
+
+
+extern void gl_DeleteTextures( GLcontext *ctx,
+                               GLsizei n, const GLuint *textures);
+
+
+extern void gl_BindTexture( GLcontext *ctx, GLenum target, GLuint texture );
+
+
+extern void gl_PrioritizeTextures( GLcontext *ctx,
+                                   GLsizei n, const GLuint *textures,
+                                   const GLclampf *priorities );
+
+
+extern GLboolean gl_AreTexturesResident( GLcontext *ctx, GLsizei n,
+                                         const GLuint *textures,
+                                         GLboolean *residences );
+
+
+extern GLboolean gl_IsTexture( GLcontext *ctx, GLuint texture );
+
+
+#endif