Bugs in date/time functions.

[Phillip Shelton <shelton usq edu au>]

Minute()
Second()
Hour()
Date2Unix()
Unix2Date()

All these functions do not respond the way an XL user expects them when the
input is an error value.

if (argv[0]->type == VALUE_ERROR)
     return value_duplicate (argv[0]);

The above two lines need to be added to each of them before the functions do
anything else.

On datevalue(),  in 1.0.4 this function works for both strings and numbers,
but on XL97 it returns #VALUE for numbers, do we want to do that?  Also
currently it returns 0 if given "Phillip", it should return #VALUE.

I can send in a diff but it will have to be tonight as I an not at my linux
box.

Phillip