Accept new Phragmén solutions if they are epsilon better + Better pre-inclusion checks. (#6173)

* part1: Accept inly epsilon better solutions

* Fix pre-dispatch check

* Fix build

* review grumbles

* Epsilon -> Threshold

substrate/primitives/phragmen/fuzzer/src/common.rs

@@ -19,8 +19,8 @@
 
 /// converts x into the range [a, b] in a pseudo-fair way.
 pub fn to_range(x: usize, a: usize, b: usize) -> usize {
-	// does not work correctly if b < 2*a
-	assert!(b > 2 * a);
+	// does not work correctly if b < 2 * a
+	assert!(b >= 2 * a);
 	let collapsed = x % b;
 	if collapsed >= a {
 		collapsed

substrate/primitives/phragmen/fuzzer/src/equalize.rs

@@ -131,7 +131,7 @@ fn main() {
 				return;
 			}
 
-			let enhance = is_score_better(initial_score, final_score);
+			let enhance = is_score_better(final_score, initial_score, Perbill::zero());
 
 			println!(
 				"iter = {} // {:?} -> {:?} [{}]",
@@ -140,6 +140,7 @@ fn main() {
 				final_score,
 				enhance,
 			);
+
 			// if more than one iteration has been done, or they must be equal.
 			assert!(enhance || initial_score == final_score || i == 0)
 		});