G29 P0 does not work as expected

[aegean-odyssey]

Buried in the discussion of issue #53 is the discovery that G29 P0 simply does not work.

@mulcmu writes:
There might be an issue going on with the G29 P0 correction. I started a print with a 3mm thick piece of acrylic placed on the bed. G29 P0 did the double tap on the acrylic which was then removed before the printing started. I expected first layer to start getting deposited 3mm above the bed, however print started on the bed surface.

@aegean-odyssey writes:
@mulcmu, your test should have produced the result you expected; that the nozzle should have stopped above the build plate. Something is not right. I'm thinking that after the G29 P0 probe, the machine is not taking up the new height value. Does homing (G28) after the G29 P0 change the outcome?

@aegean-odyssey writes:
G29 P0 does not work as advertised. Actually, it goes through all the motions and then sets the height to the value it had when it started -- it's a bug. I'll track it down. As if G29 wasn't confusing enough!

[aegean-odyssey]

Turns out to be a regression introduced in 119r12 that would affect G33 P0 and G33 P1 (aka G29 P0). It is fixed in 119r16.