Fixed issue #5: avoid using var args

Groovy being dynamic language means it cannot properly handle the situation when a single Object[] argument is given where a function expects var arg

    int foo(Object... args) { return args.length }

In Java,

    foo(new Object[3])==3
    foo((Object)new Object[3])==1

but Groovy naturally cannot do this. The use of var-args in Checker.checkedCall method was triggering this issue.
I removed var args from these methods to avoid the problem. Unfortunately Groovy doesn't support literal array syntax of
new Object[]{1,2,3}, so this involves creating a list only to convert to an array.