private FunctionInfo registerTableFunction(String functionName, FunctionType functionType,
      Class<? extends TableFunctionResolver> tFnCls, FunctionResource... resources) {
    validateClass(tFnCls, TableFunctionResolver.class);
    FunctionInfo function = new FunctionInfo(functionType, functionName, tFnCls, resources);
    addFunction(functionName, function);
    return function;
  }
Registers the UDF class as a built-in function; used for dynamically created UDFs, like
GenericUDFOP*Minus/Plus.
ql/src/java/org/apache/hadoop/hive/ql/exec/Registry.java