[TheForge] Updated hundredweight converter

[Demon Buddha]

For anyone that is interested, I've added all the necessary input 
validation routines to the converter.  Its behavior is now much nicer and 
the user can no longer input wrong data and cause the program to bomb.  
This is a good thing because it is helpful in not causing catastrophic GPFs 
and other errors that may bring your machine down.

Anyone wanting it, just say so.  I am sending a copy to Dave Brown to be 
posted on his site.

Regards,

	-Andy