Add two solutions to euler #41.

One of them (41-take2.rs) requires a still-not-accepted patch to the Rust
standard library; I'm not sure if it will ever be accepted, either.
rust-lang/rust#13761

Author: exscape

euler/41-take2.rs

@@ -0,0 +1,18 @@
+extern crate exscape;
+use exscape::is_prime;
+use std::iter::AdditiveIterator;
+
+fn main() {
+	let num = &mut[7u,6,5,4,3,2,1];
+
+	loop {
+		// Reconstruct array into a number; e.g. 7 * 10^6 + 6 * 10^5 + 5 * 10^4 + 1 * 10^0... = 7654321
+		let n = num.iter().enumerate().map(|(pos,&val)| val * std::num::pow(10u,num.len() - pos - 1)).sum();
+
+		if is_prime(n) {
+			println!("Answer: {}", n);
+			break;
+		}
+		num.prev_permutation();
+	}
+}

euler/41.rs

@@ -0,0 +1,13 @@
+extern crate exscape;
+use exscape::{primes_up_to, is_pandigital};
+
+fn main() {
+	// 8-digit and 9-digit pandigitals will all be divisible by 3,
+	// as their digital sums are divisible by 3. Therefore, none of them are prime.
+	for &p in primes_up_to(7654321).iter().rev() { 
+		if is_pandigital(p) {
+			println!("Answer: {}", p);
+			break;
+		}
+	}
+}