Add string comparison tests.

Use computed string to exercise string interning code better.

tests/basics/tests/string1.py

@@ -10,3 +10,10 @@ print('123' + "456")
 
 # iter
 print(list('str'))
+
+print('123' + '789' == '123789')
+print('a' + 'b' != 'a' + 'b ')
+
+# Not implemented so far
+# print('1' + '2' > '2')
+# print('1' + '2' < '2')