enable USE_WIN_IOCTL code unless explicitly avoided

Changes to be committed:
	modified:   doc/fixes36.1
	modified:   include/unixconf.h
	modified:   sys/share/ioctl.c

github pull request #19 made reference to resulting code behaviour
being better when windows were resized when USE_WIN_IOCTL was defined.

The logic for including the necessary enabling code in the build in
sys/share/ioctl.c was an explicit "opt-in" strategy, so anything not
deliberately and explicitly listed was not able to take advantae
of the potentially useful code. The need to add #defines to that
list would have been perpetual as new platforms came online, and
unnecessarily restrictive for everything else.

This switches the logic to include the code by default now,
and thus
unless there is an explicit "opt-out" by uncommenting
AVOID_WIN_IOCTL in include/unixconf.h

Some platforms, and we have no way of knowing which ones, may have
to ensure that AVOID_WIN_IOCTL is #define'd.

doc/fixes36.1

@@ -635,6 +635,8 @@ unix: race condition with parallel make: src/Makefile might start building
 unix: Makefile.{src,utl} ignored CPPFLAGS which is expanded by the default .c
 	rule by GNU make so if user had a value for that in the environment,
 	it would apply to some files but not others; explicitly override it
+unix: enable code guarded by USE_WIN_IOCTL by default unless prevented by
+	uncommenting #define AVOID_WIN_IOCTL in include/unixconf.h
 win32gui: getversionstring() was overflowing the provided Help About buffer
 win32gui: guard against buffer overflow in in mswin_getlin()
 win32gui: handle menu_color attribute