test(tests/lean/run): add simple overloading test

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>

tests/lean/run/e6.lean

@@ -0,0 +1,33 @@
+
+precedence `+`:65
+
+namespace nat
+  variable nat : Type.{1}
+  variable add : nat → nat → nat
+  infixl + := add
+end
+
+namespace int
+  using nat (nat)
+  variable int : Type.{1}
+  variable add : int → int → int
+  infixl + := add
+  variable of_nat : nat → int
+  coercion of_nat
+end
+
+using int
+using nat
+
+variables n m : nat
+variables i j : int
+
+check n + m
+check i + j
+check i + n
+check i + n + n + n + n + n + n + n + n + n + n + n +
+      n + n + n + n + n + n + n + n + n + n + n + n +
+      n + n + n + n + n + n + n + n + n + n + n + n +
+      n + n + n + n + n + n + n + n + n + n + n + n
+
+