[Development] Backporting the "stop unloading plugins" change to 5.6

[André Pönitz]

On Thu, Oct 13, 2016 at 08:01:57PM +0300, Konstantin Tokarev wrote:
> > I still consider the approach of not unloading plugins fundamentally
> > wrong. It only deepens the trench between Qt and valid approaches at
> > software architectures.
> 
> I think not unloading plugins is fundamentally right thing to do, if
> user does not request unload explicitly.

What should happen *if* the user requests unloading explictly?

Andre'

PS:

> * It's not supported on all platforms (e.g., uclibc and musl implement
> dlclose() as a stub).

Qt was never about providing common subsets of all supported platforms.

> * At application exit OS will unload plugins and clean up related
> resources much faster than it could be implemented with unload in
> destructors.

I am not concerned about toy applications that gets started and closed
by the minute.