This is aimed at Slic3r's spiral vase mode which continuously lifts Z.

Preventing prontserve from sending M105 temperature polling requests while the printer is heating up (M109 / no 'ok' received).

The if f >= 0 could be have been accessed even though f had not been
assigned (if float(l) failed)

Improving prontserve's temperature events. Resetting the printer on prontserve estop. Estopping on initial connection by default to kill off stray m109s.