Using equal instead of (==) solve the problem of the last commit

Switch typesTest from OUnit to OUnit2 (mostly to get a correct exit value)

tests/libtest/tallyingTest.ml

-open OUnit
+(* TODO: Switch to OUnit2 when tests are fixed, then use tools/install_hooks.sh -d to check tallying before a commit *)
+open OUnit(*2*)
 open Types
 
 let parse_typ s =
@@ -490,7 +491,7 @@ let suite =
   ]
 
 let main () =
-  OUnit.run_test_tt_main suite
+  OUnit(*2*).run_test_tt_main suite
 ;;
 
 main ()

tests/libtest/typesTest.ml

-open OUnit
+open OUnit2
 
 let parse_typ s =
   let st = Stream.of_string s in
@@ -308,7 +308,7 @@ let all =
   ]
 
 let main () =
-  OUnit.run_test_tt_main all
+  OUnit2.run_test_tt_main all
 ;;
 
 main ()

types/types.ml

@@ -549,7 +549,7 @@ let cup x y =
       absent= x.absent || y.absent;
       toplvars = TLV.empty
     } in
-    let isvar = (is_var x && x == t) || (is_var y && y == t) in
+    let isvar = (is_var x && equal x t) || (is_var y && equal y t) in
     update_tlv x y { t with toplvars = { t.toplvars with TLV.isvar = isvar }}
 
 let cap x y =
@@ -566,7 +566,7 @@ let cap x y =
       absent= x.absent && y.absent;
       toplvars = TLV.empty
     } in
-    let isvar = (is_var x && x == t) || (is_var y && y == t) in
+    let isvar = (is_var x && equal x t) || (is_var y && equal y t) in
     update_tlv x y { t with toplvars = { t.toplvars with TLV.isvar = isvar }}
 
 let diff x y =
@@ -583,7 +583,7 @@ let diff x y =
       absent= x.absent && not y.absent;
       toplvars = TLV.empty
     } in
-    let isvar = (x == any && is_var y) || (is_var x && y == empty) in
+    let isvar = (equal x any && is_var y) || (is_var x && equal y empty) in
     update_tlv x y { t with toplvars = { t.toplvars with TLV.isvar = isvar }}
 
 (* TODO: optimize disjoint check for boolean combinations *)