tmpfiles: when processing lines, always process prefixes before suffixes

tmpfiles: when processing lines, always process prefixes before suffixes

If two lines refer to paths that are suffix and prefix of each other,
then always process the prefix first, the suffix second. In all other
cases strictly process rules in the order they appear in the files.

This makes creating /var/run as symlink to /run a lot more fun, since it
is automatically created first.