Rationale:
* Logging to STDERR enables separation of processable output (e.g.,
`--version` or `--help`) and ephemeral status/error messages.
* A single file descriptor for all log messages makes it easier for
users to capture all log messages.
* Consistency: it's what most utilities do.
`$config{$h}{'status'}` was always initialized to a non-`undef` value,
so the `//` fallbacks never did anything. Instead, any protocol that
does not explicitly update the legacy `status` variable (such as
`godaddy`) would always appear to have failed even if it had
succeeded.
Change the `status*` variables to `undef` by default, and only set
them when an attempt is made so that the legacy `//` fallback works as
expected.
This shouldn't matter in practice because the `status-ipv$ipversion`
field is initialized to a non-`good` value so failing to set it to
`bad` doesn't turn it `good`, but it improves readability.
The `dnsexit2` protocol reads the IP addresses from the new `ipv4` and
`ipv6` variables, so it should update the `status-ipv4` and
`status-ipv6` variables.
Perl version strings are flawed in a few ways. Convert them to
user-friendly strings when printed so that Git tags and tarball names
are easier for downstream distributions to work with.
Passing `--version=short` simply prints the version and exits. This
will make it possible for a future commit to change `configure.ac` to
extract the version string from `ddclient.in` to avoid maintaining the
same version string in two places.
This prevents the `%builtinweb` or `%builtinfw` skip defaults from
overriding a user's explicitly empty `--web-skip=` or `--fw-skip=`
setting.
This is technically a backwards-incompatible change: Any config that
explicitly sets `--web-skip` or `--fw-skip` to the empty string but
depends on the built-in skip behavior will fail. This is unlikely to
affect many (if any) users; compatibility concerns are believed to be
far less significant than the potential need to turn off the built-in
skip.
`--arg` is preferred over `-arg` because the broader convention is to
use double hyphens for long option names. Perl accepts either.
`--arg` is preferred over `arg` to avoid confusion between `--use=ip`
and `--ip` and similar option pairs.
The `ciscov4`, `ciscov6`, `cisco-asav4`, and `cisco-asav6` strategies
were never implemented, and it doesn't make sense to implement them
because the `v4` and `v6` variants don't follow the pattern
established by the `%builtinfw` strategies.
The `%builtinfw` strategies were never implemented for `--usev6`.
