Add a failing test for #show with -short-paths.

testsuite/tests/tool-toplevel/show_short_paths.ml

@@ -0,0 +1,19 @@
+(* TEST
+   flags = " -short-paths "
+   * expect
+*)
+
+(* This is currently just a regression test for the bug
+   reported here: https://github.com/ocaml/ocaml/issues/9828 *)
+
+#show list;;
+[%%expect {|
+type 'a list = [] | (::) of 'a * 'a list
+|}];;
+
+type 'a t;;
+#show t;;
+[%%expect {|
+type 'a t
+type 'a t
+|}];;