mesa: add new signed rgba texture format
This is a (partial) backport of the signed texture format support in OGL 3.1.
Since it wasn't promoted from an existing extension roll our own.
diff --git a/docs/extensions.html b/docs/extensions.html
index dbb8eba..91ed20e 100644
--- a/docs/extensions.html
+++ b/docs/extensions.html
@@ -24,6 +24,7 @@
<LI><A HREF="MESA_resize_buffers.spec">MESA_resize_buffers.spec</A>
<LI><A HREF="MESA_set_3dfx_mode.spec">MESA_set_3dfx_mode.spec</A>
<LI><A HREF="MESA_sprite_point.spec">MESA_sprite_point.spec</A> (obsolete)
+<LI><A HREF="MESA_texture_signed_rgba.spec">MESA_texture_signed_rgba.spec</A>
<LI><A HREF="MESA_trace.spec">MESA_trace.spec</A> (obsolete)
<LI><A HREF="MESA_window_pos.spec">MESA_window_pos.spec</A>
<LI><A HREF="MESA_ycbcr_texture.spec">MESA_ycbcr_texture.spec</A>