provide a global temporary directory

provide a global temporary directory

The standard procedure 'tmp=mktemp; trap "rm $tmp" 0' was broken with the
introduction of the pager. Which overwrites the trap itself to close and
remove the pager fifo.

Now tg provides a temp playground and all other temp files should be created
inside this directory and only this directory will be removed with the exit
trap. setup_pager still overwrites the trap, but keeps the rm command from
the global temp directory. To simplify this the new function get_temp() is
provided.

Signed-off-by: Bert Wesarg <bert.wesarg@googlemail.com>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>