i965: Turn on ARB_depth_buffer_float by default.

Everything about this that we have tests for works except for the
deprecated metaops.  The conclusion we came to on IRC sounded like we
were OK with turning it on as long as core functionality works.  The
remaining failures (copypixels, drawpixels) should just be a matter of
finishing the MapRenderbuffer for them.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/mesa/drivers/dri/intel/intel_extensions.c

@@ -113,8 +113,7 @@ intelInitExtensions(struct gl_context *ctx)
 
    if (intel->gen >= 4) {
       ctx->Extensions.ARB_color_buffer_float = true;
-      if (override_version >= 30)
-	 ctx->Extensions.ARB_depth_buffer_float = true;
+      ctx->Extensions.ARB_depth_buffer_float = true;
       ctx->Extensions.ARB_depth_clamp = true;
       ctx->Extensions.ARB_fragment_coord_conventions = true;
       ctx->Extensions.ARB_fragment_program_shadow = true;