While looking to fix a different bug here, I found the current
state of things where we had a mix of fd-relative API versus not
frustrating.
Change the code around to consistently use *at, and also add some more
tests.
This large patch moves the core xattr logic down into libgsystem,
which allows the gs_shutil_cp_a() API to copy them. In turn, this
allows us to just use that API instead of rolling our own recursive
copy here.
As noted in the new comment though, one case that we are explicitly
regressing is where the new /etc removes a parent directory that's
needed by a modified file. This seems unlikely for most vendors now,
but let's do that as a separate bug.
https://bugzilla.gnome.org/show_bug.cgi?id=711058
Colin Walters