Fixed position.txt not getting created if 'import hal' used in python remap code. Fixes issue #244.

The Python hal module steals SIGTERM away from the handler set in milltask.
Milltask relies on getting SIGTERM from the 'liunxcnc' script (via 'kill') to
write out position.txt and exit. Milltask now looks to see if the SIGTERM
handler changed during init, then sets it back to its original handler which
in turn calls the thief's handler as well as exiting normally and writing
out the position.txt file.