mesa: improved error msg
diff --git a/src/mesa/shader/shader_api.c b/src/mesa/shader/shader_api.c
index 38f4cd0..828d3f0 100644
--- a/src/mesa/shader/shader_api.c
+++ b/src/mesa/shader/shader_api.c
@@ -1469,7 +1469,8 @@
          return;
       }
       if (!shProg->LinkStatus) {
-         _mesa_error(ctx, GL_INVALID_OPERATION, "glUseProgram");
+         _mesa_error(ctx, GL_INVALID_OPERATION,
+                     "glUseProgram(program %u not linked)", program);
          return;
       }
    }