Test case where random sample is popFront'ed before being read.

  * Some rough-and-ready statistical checks ensure that the
    numbers being generated fall within acceptable limits.
    It's a safety check rather than a rigorous statistical
    analysis. ;-)

  * This test acts as a trigger case for an issue with the
    previous patch: if the function delegate skip() is initialized,
    a foreach() loop will take a (value-type) copy of the sample
    but the delegate therein will point to the original, generating
    nonsensical numbers.  This issue will be fixed in the next patch.
Fix the delegate issue in patch e6b7e1f4c0ac63417c78f2d916fe5ada871250bb

  * The delegates were causing the sampling process to fail if a
    sample was ever passed/copied by value (e.g. in a foreach loop)
    after the value of the delegate had been set: the delegate would
    continue to point to the data in the original, and so generate
    spurious values.

  * This neat little trick to rescue the delegate approach was suggested
    by Artur Skawina in D.learn:
    http://forum.dlang.org/post/mailman.796.1378134173.1719.digitalmars-d-learn@puremagic.com