bpo-29176 Use tmpfile() in curses module (#235)

The curses module used mkstemp() + fopen() to create a temporary file in
/tmp. The /tmp directory does not exist on Android. The tmpfile()
function simplifies the task a lot. It creates a temporary file in a
correct directory, takes care of cleanup and returns FILE*.

tmpfile is supported on all platforms (C89, POSIX 2001, Android,
Windows).

Signed-off-by: Christian Heimes <christian@python.org>