* Eliminates recursive calls inside AP_Param.
This is important to Pat @ Galois, but not the project in general.
Recursion depth on these functions is bounded structurally using
existing nested group constructors (can't create loops in finite space)
and checked at init time
We would like to be able to use Vector3f as a parameter while exposing
the individual elements of the vector as MAVLink parameters. This
change to AP_Param makes that possible, by giving AP_Vector3f a dual
personality
adding a idx element to the GroupInfo will make it less likely that a
developer will change the IDs of group elements, and make it easier to
see that these IDs are important for identifying a variable in EEPROM
The header packing has changed to make it 24 bits on all platforms,
which allows us to lower the EEPROM variable max size to 1024 bytes
again
Andrew Tridgell
Pat Hickey