Add an advisory interruption mechanism to QThread.

To ease interruption of long running tasks, a new method
QThread::setInterruptionRequested() can be called.
The task can check QThread::isInterruptionRequested()
and act upon it by stopping itself.

These methods are designed to replace the use of a global variable
and other hacky ways to stop a task running in another thread.

Change-Id: I17622dd60d2262078210e7e4294ad6c53a6dc179
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Revert "Implement move-ctor and move-assignment-op for QScopedPointer"

This reverts commit 5b9006bbdba7dcab01b8e640554a7d7a4b64f76b.

Also revert "Doc: Enable documentation for QScopedPointer's rvalue ref functions"

This reverts commit 5f8416ec659b134db90df7e7f857db77fd27b6ab.

Adding a move contructor to QScopedPointer makes no sense, because moving
means 'escaping the scope', which breaks the fundamental point of
QScopedPointer.

Change-Id: I4ac1b108bf199af6e436fa1629aa2d3b93c27724
Reviewed-by: Lars Knoll <lars.knoll@digia.com>