Thats plenty clear, isnt it? As soond as kdbus is merged into kernel, systemd will depend on it, and then if I need to go back to older kernel, I have to downgrade systemd as well?
Why do you downgrade your kernel?
systemd has to be pinned to -1 or your servers will get upgraded to it without any interaction from your part.
Of course it gets installed, it's the default init system in Jessie. Most users would expect to have it installed when upgrading, considering that it's a major new feature in Jessie and meant as a replacement for sysvinit.
Beware also that Apache configurations change.
Apache went from 2.2 to 2.4, which in Apache speak is pretty much a major version change. There were lots of changes in 2.4, especially making the event-based mpm the default. But there's also a lot of other changes so expect that you have to go through and possibly change a lot of configuration. I also have a number of custom Apache modules that had to be partly rewritten. But once that was done things have been running just fine.
Not to mention the Windows-like version numbering scheme!
...gnu11 instead of the older gnu89
Blame ISO. The gnu compiler modes named in the same scheme as the corresponding versions of the C programming language, C89, C99, C11.
Link to Original Source