The OLPC mesh code did rely on nm_manager_get() referencing the
singleton when returning it, but all other callers of nm_manager_get()
did not.  Thus the manager's refcount would always increase and
almost never decrease.  Fix the refcounting so that the manager
always has only one ref, and it's lifetime is controlled by
main() and nothing else.

Use the glib wrapper for snprintf.

Signed-off-by: Thomas Haller <thaller@redhat.com>

So far NetworkManager didn't tell which option it didn't know about:

  Invalid option.  Please use --help to see a list of valid options.

Now it is a bit more informative:

  Unknown option --asdf.  Please use --help to see a list of valid options.

The "Unknown option" string is marked as translatable in glib so i18n
doesn't suffer.

Signed-off-by: Thomas Haller <thaller@redhat.com>

If the command line or NetworkManager.conf mentions a non-existent
domain, just print a warning and ignore it. That way if you switch to
using an older NM that doesn't have that domain, it will still work.

and ensure that main() frees the singleton before exiting

libgsystem contains more than just the local allocation macros; in the
future we will likely want to make use of some of this such as the
structured logging support.

And make it owned by NMManager, rather than being a separate top-level
object.

Useful to see which files are being read.

The new setup phase goes like this:

- main()
- parse command line options
- logging is configured, targeting stdout/stderr
- ...other stuff...
- do or do not daemonize, depending on commandline option and config files
- Call openlog() - further log messages go to syslog (and potentially
  stderr as well, if the -d option was specified so we use LOG_PERROR).

Basically, this allows us to log messages about config file parsing
and such, which *greatly* helps with debugging.