Check that function exists

[Skitty]

I would say a function that checks if a user defined function and/or a native Autoit function exists would be a little useful, PHP has such a function and I've found it useful in various occasions, one reason I'm looking for such functionality now is due to a UDF I'm attempting to create that will be supplied with a users own function to be called and checking to see if the functions exists without running it would be great.