This reverts commit 9eee15917e01a89d937d1cba2eebbe9d65daeb72.  As agreed
with David Faure, we are going to leave this change in place for 5.7 and
see what happens.

CCMAIL: faure@kde.org
CHANGELOG: Reverts previous commit, both can be left out of the changelog.

On further reflection, introducing a SIC to fix the bug is not ideal.  I'm
working on something that will address the underlying bug, but I didn't have
it in time for 5.7.

The versioning behaviour is left, as I do want it to exist for the future.
This only reverts the mandatory versioning of files to avoid the compatibility
break.

CHANGELOG: Undo 915976c123, which never saw a release, enough to avoid the SIC.

This patch is necessary because:
When we use kf5 + kde4 application, kconf_update which launchs at the start when we launch kde.
But it will migrate some config file, for example it will show that we need to migrate konversation
so it will create a konversationrc in .config/

But when we launch konversation there is a kdelibs4migrator which wants to migrate settings and config in .config
but it shows a konversationrc in .config so it will never migrate and we will lose all settings.

So we can force to remove all .upd in kf5 but it will not fix problem during migration or when we have kde4 application
install in same directory as kf5.

So now I force for each upd file to have a "Version=5" so kconf_update (kf5) will migrate just kf5 upd file and it will fix my bugs.

REVIEW: 121797
CHANGELOG: Now kconf_update doesn't process upd file from kde4. We need to add "Version=5" in top of the upd file otherwise it will be skipped.

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

REVIEW: 118666

Previous code said if we found an executable in kconf_update_bin
try to find a different executable in the normal path

Reviewed-by: Rohan Garg

We get a CMake warning for reading the LOCATION property, but I don't see
how else to do it (generator expressions don't seem to work)

This allows removing some custom WIN32 API code and is also nicer than
directly calling system()

This is for the benefit of kded, which needs to run this binary.

REVIEW: 117023