Disable mipmap filtering by default in texture materials.

15999f14f146b5c04fb40b31b69ceeeece273430 changed QSGPlainTexture so it
allows mipmap filtering by default. This requires a call to
glGenerateMipmap() for textures to be valid, if mipmap filtering is
used. Our texture materials follow the GL default which is to use the
somewhat useless GL_NEAREST_MIPMAP_NEAREST. As a result we've had a
number of bugs where textures are used and the call to
glGenerateMipmap() is omitted. This happens for instance when using
QQuickTexture::createTextureFromId().

Generating mipmaps by default is also a serious performance regression.

To remedy this and minimize the impact on existing code, we disable
mipmapping by default.

[ChangeLog][QtQuick][SceneGraph] QSGTextureMaterial and
QSGOpaqueTextureMaterial uses QSGTexture::None as default mipmap mode.

Task-number: QTBUG-38321
Change-Id: Ia9d09fbcf710efb4575938053d0a2046f604a197
Reviewed-by: Caroline Chao <caroline.chao@digia.com>
Reviewed-by: Laszlo Agocs <laszlo.agocs@digia.com>
Regenerate mipmaps after changing the imagedata of a texture.

This has been a latent bug since the class was written, but has
only surfaced after 15999f14f146b5c04fb40b31b69ceeeece273430 when
mipmapping was allowed for all QSGPlainTextures.

Task-number: QTBUG-38321
Change-Id: I058e554c4035c573d2ddb4ea793d8ad53e11e54b
Reviewed-by: Laszlo Agocs <laszlo.agocs@digia.com>
Stabilize tst_qqmlxmlhttprequest::stateChangeCallingContext() on Mac.

Fix fails:
tst_qqmlxmlhttprequest::stateChangeCallingContext() '(object->property("success").toBool() == true)' returned FALSE. ()

Debugging reveals that in most cases the function loadComponent()
is only called with parameter which=1; the call with parameter
which=0 never triggers.

Change-Id: I3c9c2f618d52c2bc8dd584a5fc3ab2f115715381
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
Mark tst_qquicktextinput as insignificant on Mac OS X

This will allow further integrations until QTBUG-38363 is fixed.

Change-Id: I277628c55b893d199bd1886ee6eb9ff466860a05
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@digia.com>