Add opt-out environment variable for @2x images

There are cases where @2x images are in use but
where you don't want the associated behavior:
- You are implementing an image editor
- You are inheriting a resource set which has @2x
  images, but don't want that behavior with Qt.

Add support for disabling @2x behavior with QT_HIGHDPI_DISABLE_2X_IMAGE_LOADING.

Change-Id: I206e050b6241f8935b4404c7a28b024a9e00d46c
Task-id: QTBUG-38485
Reviewed-by: Jake Petroules <jake.petroules@petroules.com>
Reviewed-by: Morten Johan Sørvig <morten.sorvig@digia.com>
Move QXmlReaderPrivate to private header.

First step for making QXmlSimpleReader reentrant.

Task-number: QTBUG-40015
Change-Id: I1666672b1759adb745b86ce58488142f3c66d3f5
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Make QDom/QXmlSimpleReader reentrant.

I moved the evil static bool to QXmlSimpleReaderPrivate, and used
it from QDom, when the reader instance is a QXmlSimpleReader
(if it's not, nothing happens, like before).

Task-number: QTBUG-40015
Change-Id: I54ba89db334d7b086379c4a6840cf0de23f77027
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
QPdf::addImage(): avoid a QImage detach when it's in an acceptable Format

Don't detach QImage, when it's in Format_Mono or Format_ARG32.
Use QImage::constScanLine() instead of QImage::scanLine().

Change-Id: I30fcafb576aea3189637a40fd75f77c70017ba46
Reviewed-by: John Layt <jlayt@kde.org>
Reviewed-by: Gunnar Sletta <gunnar.sletta@jollamobile.com>
Accessibility Linux: Fix crashes when accessing invalid functions

There is no way to prevent ATs from calling random functions on DBus.
While these functions shouldn't exist when we don't advertise the
interface, they should just fail gracefully.

Task-number: QTBUG-40044
Change-Id: Ia29b49b16feabc0beb80007456e53497f230c7d4
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@digia.com>
Doc: fix a link in QAbstractOpenGLFunctions documentation

Change-Id: Icc0109de22de756f7e4b3e888b0ee28a9b9c04d5
Reviewed-by: Sean Harmer <sean.harmer@kdab.com>
Fix debug output of QTouchEvent.

Return dbg.space().

Task-number: QTBUG-29946
Change-Id: Ia79b297ee3801ccba9f7b1c22ac7a8761cbe8b2e
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>
Improve QListWidget documentation.

Mention that removeItemWidget() isn't sufficient to remove a row.
List related functions so that it's easy to see the relation
between them.

Change-Id: Ia1d467390f00976e2276d50df35dd555f7992a9a
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>