When using placement new placement delete must also be defined

At least MSVC2013 otherwise reports a warning. Also see discussion here:
http://social.msdn.microsoft.com/Forums/vstudio/en-US/a5b5305d-551c-4b79-badc-2989ac11b8a5/the-usage-of-placement-new-produces-a-c4291-warning?forum=vclanguage

Change-Id: I1026b2ff5910d3af9d496621d0831bea9c8f116d
Reviewed-by: Sean Harmer <sean.harmer@kdab.com>