Add 64 bit data types to Igor

I just want to re-iterate what is hinted at in http://www.igorexchange.com/node/2550 : It would be great to have 64 bit integer data types (signed and unsigned) fully integrated in Igor.
I'm aware of http://www.igorexchange.com/node/5397 , but native int64 / uint64 support would be much cleaner.

- Fabrizio