I broke "GETCONF *Port" in 20956, when I made SocksPort a
subordinate option of the virtual option SocksPortLines, so that I
could make SocksPort and __SocksPort provide qthe same
functionality. The problem was that you can't pass a subordinate
option to GETCONF.
So, this patch fixes that by letting you fetch subordinate options.
It won't always be meaningful to consider these options
out-of-context, but that can be the controller-user's
responsibility to check.
Closes ticket 21300.
