QWinOverlappedIoNotifier: Add an extended waitForAnyNotified() method

The existing waitForNotified method has the design limitation that it
doesn't allow the tracking of multiple I/O operations on a single
file handle.

Therefore we introduce an additional method waitForAnyNotified that
returns a pointer to the triggered OVERLAPPED object.

Change-Id: I536ed7f6828daa2b0ce03f2d662eeb10aa89ca99
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>
qscopedvaluerollback: add convenience constructor

It's a common need to assign a variable to something when entering a
code block, and then revert it upon exit. qscopedvaluerollback can
be used for this. But as a convenience, this patch adds an
extra constructor so that you can "protect" and set a variable
in one go instead of using two lines.

Change-Id: If4b89d3a5ba32ef2304bda058b1b6050932612ed
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>