Description:
------------
Using the collator for a big set of IDs generated from three fields like

`sprintf('%010d#%s#%s', $someSmallNumber, $word1, $word2)`

Sorting this with Collator will provide the expected results if the ID starts with a word, however for numeric prefix sorting will fail.

Tested on 5.5.17-2+deb.sury.org~trusty+1 (cli) and 5.5.15-2+deb.sury.org~trusty+1 (cli) on vagrant VM and native ubuntu 14.04. with different data sets.

Sorting by the first key works fine, by secondary key fails. Using a space or other separator does not have any effect for the tested data set.

Test script:
---------------
<?php

$c = new Collator("en_US"); // should work with any locale

$a = ["02#aa", "02#ab", "03#a", "02#a", "03#x", "03#b", "03#ba", "03#b", "04#a", "03#f"];

echo 'collator sort:' . PHP_EOL;
$c->sort($a, SORT_STRING); // SORT_REGULAR produces same result
var_dump($a);

echo 'expected results:' . PHP_EOL;
sort($a, SORT_STRING);
var_dump($a);'

Expected result:
----------------
array(10) {
  [0] =>
  string(4) "02#a"
  [1] =>
  string(5) "02#aa"
  [2] =>
  string(5) "02#ab"
  [3] =>
  string(4) "03#a"
  [4] =>
  string(4) "03#b"
  [5] =>
  string(4) "03#b"
  [6] =>
  string(5) "03#ba"
  [7] =>
  string(4) "03#f"
  [8] =>
  string(4) "03#x"
  [9] =>
  string(4) "04#a"
}


Actual result:
--------------
array(10) {
  [0] =>
  string(4) "02#a"
  [1] =>
  string(5) "02#ab"
  [2] =>
  string(5) "02#aa"
  [3] =>
  string(4) "03#b"
  [4] =>
  string(4) "03#f"
  [5] =>
  string(5) "03#ba"
  [6] =>
  string(4) "03#x"
  [7] =>
  string(4) "03#b"
  [8] =>
  string(4) "03#a"
  [9] =>
  string(4) "04#a"
}