docs/specs: annotate MESA_set_3dfx_mode as obsolete

Aimed to work with Glide, which hasn't been a thing in over 10 years.
There are no drivers that implement it, so annotate it as obsolete

v2: Move the extension to OLD/

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Brian Paul <brianp@vmware.com> (v1)
Reviewed-by: Adam Jackson <ajax@redhat.com> (v1)
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>

docs/specs/OLD/MESA_set_3dfx_mode.spec

@@ -0,0 +1,85 @@
+Name
+
+    MESA_set_3dfx_mode
+
+Name Strings
+
+    GLX_MESA_set_3dfx_mode
+
+Contact
+
+    Brian Paul (brian.paul 'at' tungstengraphics.com)
+
+Status
+
+    Obsolete.
+
+Version
+
+    Last Modified Date:  8 June 2000
+
+Number
+
+    218
+
+Dependencies
+
+    OpenGL 1.0 or later is required.
+    GLX 1.0 or later is required.
+
+Overview
+
+    The Mesa Glide driver allows full-screen rendering or rendering into
+    an X window.  The glXSet3DfxModeMESA() function allows an application
+    to switch between full-screen and windowed rendering.
+
+IP Status
+
+    Open-source; freely implementable.
+
+Issues
+
+    None.
+
+New Procedures and Functions
+
+    GLboolean glXSet3DfxModeMESA( GLint mode );
+
+New Tokens
+
+    GLX_3DFX_WINDOW_MODE_MESA	    0x1
+    GLX_3DFX_FULLSCREEN_MODE_MESA   0x2
+
+Additions to Chapter 3 of the GLX 1.3 Specification (Functions and Errors)
+
+    The Mesa Glide device driver allows either rendering in full-screen
+    mode or rendering into an X window.  An application can switch between
+    full-screen and window rendering with the command:
+
+	GLboolean glXSet3DfxModeMESA( GLint mode );
+
+    <mode> may either be GLX_3DFX_WINDOW_MODE_MESA to indicate window
+    rendering or GLX_3DFX_FULLSCREEN_MODE_MESA to indicate full-screen mode.
+
+    GL_TRUE is returned if <mode> is valid and the operation completed
+    normally.  GL_FALSE is returned if <mode> is invalid or if the Glide
+    driver is not being used.
+
+    Note that only one drawable and context can be created at any given
+    time with the Mesa Glide driver.
+
+GLX Protocol
+
+    None since this is a client-side extension.
+
+Errors
+
+    None.
+
+New State
+
+    None.
+
+Revision History
+
+    8 June 2000 - initial specification