releaseme new requirement: non-conflicting files on case-insensitive FS/OS

[Harald Sitter]

Guten Abend Everyone!

To aid with use of our tarballs on Windows and case-insensitive file
systems, releaseme now makes sure [1] that the tarballs it generates
are safe to use in such contexts.

As this is a major problem for pretty much every source tarball as it
prevents people from doing Windows builds and/or unpack on exfat/fat32
this is considered a fatal flaw in the tarball. To that end if you use
releaseme you may want to run tarme now so your next release doesn't
get held up by case-insensitive file conflicts.

If you have any questions please do ask.

[1] https://phabricator.kde.org/R572:0936ab0e02551fe6d3e8ad07b97cd7d7d3d26838

HS