goption: Don't include parsed option values in G_OPTION_REMAINING

After a call to g_option_context_set_ignore_unknown_options(context, TRUE),
the values of short options were included in the array returned by a
G_OPTION_REMAINING option.

https://bugzilla.gnome.org/show_bug.cgi?id=729563
Add a testcase for the previous fix

This testcase tests that short option arguments are
not erroneously added to the remaining argument array
when g_option_context_set_ignore_unknown_options is
called.
https://bugzilla.gnome.org/show_bug.cgi?id=729563