This enables the mainConfig optimization in all threads,
and ensures the user warning only happens in the main thread.

The test-mode-enabled logic is only really useful in the main thread,
but it's simpler to just do it in all threads.

REVIEW: 118985

Visual C++ 2010 throws an internal compiler error trying to compile
kconfigtest, since 5f4dc2973f. I couldn't figure out a non-intrusive
code tweak that would work around the ICE, so I had to skip compiling
this particular initialization code on this particular compiler version,
and skip running the test that relies on it (testEnums).

The dummy=42 entry is so that the config group isn't empty,
which makes testGroupCopyTo and testReparent still run and pass,
so we don't need to skip them.

REVIEW:118852

- QLocale::QLocale::Austria
+ QLocale::Austria

I'm surprised this worked in gcc in the CI...

NAME_PREFIX now only changes the test name, not the target name.

This fixes a regression introduced in
988f09bb051dca0437ecec431ee44ed5b4a560d8.

The mentioned commit ensures that if the locale is e.g. "de_DE" the
entry "de" will be used. But this breaks if there is a translation
for another country. E.g. for "de_CH" it would also pick the "de"
entry.

This change now operates on both just the language code and the locale.
If an entry with the language code is present it will be picked. If
another entry with the exact locale is found it will be overwritten.
Modifiers are not supported as this is currently missing in QLocale.

REVIEW: 118692

Some tests are testing underlying components, these should be tested
before testing the components that depend on them.

REVIEW: 118680

The underlying KConfig used QLocale::name() for getting the locale
aware part. But this returns "de_DE" while the desktop files store
"de".

In addition it constructs a QLocale object instead of using the
system locale. This has the advantage that the usage of
QLocale::setDafault() gets honored by KConfig.

REVIEW: 118564

- use Q_NULLPTR instead of 0 or NULL
- simplify some foreach loops
- use QStringLiteral in a few places
- added a few consts

REVIEW: 118666

Simplify KConfigGroup::readEntry/writeEntry.

KConfigGroup::readCheck/writeCheck caused some compilers to complain
since they were private functions that were being reimplemented outside
the class definition.

Updated KCONFIGGROUP_DECLARE_ENUM_QOBJECT/
deprecated global functions created in KDE4 times.