Add test of range-based seeding for Mt19937_64

As with the earlier test of range-based seeding for the 32-bit Mt19937,
this test is added purely in order to ensure consistency of behaviour in
future.  It does not appear to match the behaviour of the superficially
similar sequence-based seeding available in the C++11 <random> version
of the Mersenne Twister.

It does however match the behaviour of the `MersenneTwisterEngine`
implementation available in `hap.random`, which was derived from the
`Boost.Random` implementation, but whose range-based seeding was copied
from Phobos.  This would suggest that any divergence with C++11 is down
entirely to the seeding mechanism.

Author: WebDrake

std/random.d

@@ -901,6 +901,10 @@ alias Mt19937_64 = MersenneTwisterEngine!(ulong, 64, 312, 156, 31,
     assert(gen.front == 14514284786278117030uL);
     popFrontN(gen, 9999);
     assert(gen.front == 9981545732273789042uL);
+    try { gen.seed(iota(312uL)); } catch (Exception) { assert(false); }
+    assert(gen.front == 14660652410669508483uL);
+    popFrontN(gen, 9999);
+    assert(gen.front == 15956361063660440239uL);
 }
 
 @safe unittest