Add support to SDL and GDI modes for CONIO_OPT_DISABLE_CLOSE

... to disable the OS or Window Manager's "close" app icon/control/option
which attempts an ungraceful termination of UIFC apps (e.g. SCFG) and does
weird and wonderful things (e.g. infinite loops which are invisible on
Win32-GDI, so you end up with a ghost/zombie process).

Disabling the OS/WM close option is an alternative solution to checking
uifc.exit_flags & UIFC_XF_QUIT everywhere you need to to avoid a
looping/zombie process.

Next up X11, which appears I need to remove _NET_WM_ACTION_CLOSE
from the _NET_WM_ALLOWED_ACTIONS Atom... ?