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.
Clever.  Makes things more interesting, as Egyptian(1+p/q) is not the same as Egyptian(p/q) with some prefix, and Egyptian(2+p/q) is something else altogether.  But it isn't clear how the other algorithms would handle this, since it's essentially a greedy operation.  Probably best just to reject invalid inputs, I agree.