So currently on one intel tester find_tests is failing the 'pos !=
x.end()' test, but not the 'const_pos != x_const.end()' test for
unordered_set (and possibly others, the test results are truncated). I'm
a bit stumped as to why this should be, as for unordered_set the const
and non-const versions are basically the exact same code. See if
changing the order makes any difference to what fails.