Make it possible to route messages to syslog
Rip out error codes

As it turns out, they're rather annoying to maintain, and we don't even need
them.  They also clutter the code unnecessarily in their current form.

If it ever comes to having to have them, let's make another version of
error_set(), maybe error_set_with_code(), that makes it possible to also set
an integer within `struct error'.

The only problem with the above solution is when we aggregate errors from
multiple functions (be it by calling one after another, or through nesting of
functions that may return an error).

But let's care about that when the time comes for it.
Cleanup

No functional changes.
First bugfixes

Now we can at least successfully register.