Peter Hall

Rebased and added a auto test which fails on master and passes with this PR.

I have reworked to take a pos control pointer from copter which allows the constrain to pos control limits to be done inside AC_Avoid resulting in a much smaller change....

> I'm slightly surprised that the vertical speed limits weren't being applied in AC_PosControl but perhaps that's because we are not using "input shaping" The pos controller does not apply...

Reworked to separate the speed limit into horizontal and vertical components. I also found I had omitted to apply the Z limit in the 3D case which I have now...

We only support upto 16 RC input channels.

Do you actually want to program such moves with loiter turns, or if we were to do it automatically would what be better? It would be a big re-work, but...

One problem I found while trying this out is that because we scale the loiter radius with altitude its very hard to manually program such missions if your above sea...

> For what it's worth, I disable that altitude radius thing because we've implemented it wrong. Its meant to keep us in our flight envelope but it should be enforcing...

> Would you all consider just implementing a trajectory-following controller? I'm happy to help and start in 2D to make it more feasible. We can use the L1 controller for...

> First, because these two stress values cannot be converted one into another in a vendor-independent way. Second, because stress messages come more frequently, and status messages come roughly at...