Add tests for +

(Now that + works again.)

scm/inc/tests.scm

@@ -100,3 +100,10 @@
    ["(char? #f)" "#f\n"]
    ["(char? ())" "#f\n"]
    ])
(do-tests "3.4 - binary primitives"
  '[["(+ 1 2)" "3\n"]
    ["(+ 0 0)" "0\n"]
    ["(+ 41 1)" "42\n"]
    ["(+ 1 41)" "42\n"]
    ["(+ -10 11)" "1\n"]])