xtree cancel takes longer than 50 ms

[nickodell]

The testcase "XTree<3> cancellation" consistently fails on my system.

Reproduction

Run ./ao/test/ao-test "XTree<3> cancellation"

Output:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
ao-test is a Catch v1.1 b3 host application.
Run with -? for options

-------------------------------------------------------------------------------
XTree<3> cancellation
-------------------------------------------------------------------------------
/home/nick/ao/ao/test/xtree.cpp:212
...............................................................................

/home/nick/ao/ao/test/xtree.cpp:237: FAILED:
  REQUIRE( elapsed_ms.count() < 50 )
with expansion:
  79 < 50

===============================================================================
test cases: 1 | 1 failed
assertions: 1 | 1 failed

(The number of milliseconds it takes varies from 55 to 80.)

Removing cancel

If cancel.store(true); is commented out, the computation takes 433816 milliseconds.

End user visible impact

None known.

[mkeeter]

Okay, I've bumped that timeout a little bit, given the range that you found.