QComboBox: update focus policy when setting a new line edit

On OS X, the focus policy of QComboBox is different when editable or
not.

Task-number: QTBUG-39650
Change-Id: I394564f8a1a6d462e86d2497fe8874e6107a8a58
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@digia.com>
Reviewed-by: Jake Petroules <jake.petroules@petroules.com>
Move most of the QLibraryPrivate initialization to its constructor

This commit moves the setting of the loadHints to inside the constructor
or to QLibraryStore::findOrCreate (which is under a mutex). This avoids
data race conditions with two threads asking for the same plugin at the
same time, with different load hints.

This also opportunistically moves the setting of the error message for
empty file names.

Task-number: QTBUG-39642
Change-Id: I497a41781d10e407d6420116a0b05fdfe2b548de
Reviewed-by: David Faure <david.faure@kdab.com>
Fix warnings from MSVC 2013

qhosaddress.h(88) : warning C4224: nonstandard extension used : formal parameter 'sockaddr' was previously defined as a type

Change-Id: I38ee9dcb0d81d5ec4f71c2b50dc4f331eb61e7de
Reviewed-by: Richard J. Moore <rich@kde.org>