Bump Qt version to 5.0.2

Change-Id: I573601fb609cdb632fbb422920801a24be4c0448
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
fix build failures on mingw caused by name clash

In mingw.org, basetyps.h contains

    #define interface _COM_interface

which clashes with function parameter names in qdbusmessage.h.
Although there is no clash when building qtbase itself, the clash
makes building qttools 5.0.1 fail. Presumably this could also affect
other applications.

Taken from 2cc9a9a51d6742708b1ea41c7338755e2a0ee9e9 which solves the
same problem in another header.

Change-Id: I802d5c673b544fb3a17e9273030876928faa5c46
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Optimize code sample of QObject::isSignalConnected

Since isSignalConnected is meant to be used in performance critical
code, and that QMetaMethod::fromSignal is relatively slow, it is better
to have it a a static variable in the code sample, as a good
recommendation on how to use it.

Since QMetaMethod::fromSignal should not change during the life of the
program, it should be safe.  Also, if different threads run at the same
time, both should lead to the same result.

Change-Id: Ib6113d11ca93f216bc3a92aea4eaa4da6a4151ca
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>