This is the second and last part of the forward-port of
https://qt.gitorious.org/qt/qt/merge_requests/1281
[ChangeLog][QtConcurrent] run() now optionally takes as its first argument
the QThreadPool to run the task on.
Task-number: QTBUG-17220
Change-Id: I4b46eca6ef7de9cd34dac07e6d4b8ad830426b97
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>