tmpfiles: do not fail when copying an empty directory
tmpfiles: make sure "C" doesn't copy anything if the destination already exists

Previously it would recursively copy the entire tree in, and descend
into subdirectories even if the destination already exists. Let's do
what the documentation says and not do that.

If files down the tree shall be copied too, they should get their own
"C" lines.
units: add missing caps so that GetAddresses() can work
networkd: fix refcounting with UseMTU=yes

The link was unintentionally being unreferenced instead of referenced for the
MTU setup.
units: order systemd-tmpfiles-clean.service after time-sync.target

That way, on systems lacking an RTC we don't false start removing aged
files too early.
copy: don't eat up error from chown()/chmod()

The idea was to not fail on, nor to ignore errors from chown()/chmod(),
but to proceed and simply return the most recent error...
sd-dhcp6-client: remove bogus dependency on dhcp6-icmp6.h

Makefile.am had a reference to it but it none of the sources included it.

Tested: "make dist" works again after this patchset is applied.

Fixes: 2ea8857effb833615b16d10fc7a19a7104c19e13
sd-dhcp6-client: fix path of sd-icmp6-nd.h in Makefile.am

It was incorrectly looking for a file in src/libsystemd-network/ when the file was actually deployed to src/systemd/ instead.  This broke "make dist".

Tested: "make dist" works again after this patchset is applied.

Fixes: f20a35cc0d537dd4cfc1054cf7936b04a1700f3a
sd-dhcp6-client: include dhcp6-protocol.h in the list of sources

If the file is not listed, then "make dist" will not include it.

Tested: "make distcheck" works after this fix is applied.

Fixes: 139b011ab81ccea1d51f09e0261a1c390115c6ff
coredump: fix include of xattr.h

The correct path is now <sys/xattr.h> (from glibc-headers) and no longer
<attr/xattr.h> (from libattr-devel.)

Fixes: 34c10968cbe3b5591b3c0ce225b8694edd9709d0
sd-dhcp6-client: fix uninitialized variables
sd-icmp6-nd: fix uninitialized fd
tests: fix test-icmp6-rs

Don't close the fd given to sd-icmp6-nd, since it will be aynschonously closed
by sd_icmp6_nd_unref
tests: add missing return
tests: add tests to test-util

add tests for:
  - filename_is_safe
  - ascii_strlower
  - files_same
  - is_valid_documentation_url
  - file_in_same_dir
  - endswith
  - close_nointr
  - unlink_noerrno
  - readlink_and_make_absolute
  - read_one_char
  - ignore_signals
  - strshorten
tests: add tests for strv_extendf
util.c: simplify rm_rf_children_dangerous
units/systemd-sysctl.service.in: run after load-modules

Modules might or will register new sysctl options.

[zj: This mechanism of adding modules just to reliably set sysctl
attributes is not ideal. Nevertheless, sysctl for dynamically created
attributes is simply broken, and this is the easiest workaround.]

https://bugzilla.redhat.com/show_bug.cgi?id=1022977
https://bugzilla.novell.com/show_bug.cgi?id=725412
man: document statically loading modules for sysctl settings

https://bugzilla.redhat.com/show_bug.cgi?id=1022977
https://bugzilla.novell.com/show_bug.cgi?id=725412
man: also describe an udev rule for bridge sysctl