Make Egyptian fractions a little more robust.

Add checking for negative arguments, and arguments > 1

Don't know if this is actually needed; it does help avoid endless loops if you give an improper fraction to some of the algorithms.  Feel free to reject.
I don't see why it should; I'm removing the whole part and leaving it with the normal state of affairs to work with.  But yes, I should do and include more testing to be sure.