restoreBuiltins
Restore the values of builtin functions.
restoreBuiltins()

Description
If the value of a variable storing a builtin function object is intentionally or inadvertently set to some user defined value, the prior value can be restored by calling this function.
Example
>>sin
Builtin funcion:sin
>>sin=2
>>sin
    2
>>restoreBuiltins()
>>sin
Builtin funcion:sin