This adds some extra paranoia: when we recursively chown a directory for
use with DynamicUser=1 services we'll now drop suid/sgid from all files
we chown().
Of course, such files should not exist in the first place, and noone
should get access to those dirs who isn't root anyway, but let's better
be safe than sorry, and drop everything we come across.
This splits out a bunch of functions from fileio.c that have to do with
temporary files. Simply to make the header files a bit shorter, and to
group things more nicely.
No code changes, just some rearranging of source files.
