RobertB_MultiWii_2_2 branch - alt hold

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At least in r315 revision alt hold isn't working correctly.
Earlier version, where alt hold was working OK - r261, probably some versions 
after that or even latest release from TC branch.

I tested with low alt PID's (something like 14, 10, 20), with very high (70, 
30, 40), it's not working in any case...

Expecting: stable hover (was working in earlier TC releases with P=17, I=12, 
D=30) within 1m height (if wind won't disturb). Yes, baro (and acc) is covered 
with soft foam and it was working good before.
Actual result - hover with throttle and acc (horizon) mode on, turn on baro. 
Copter will tilt to it's back (not a lot, but noticeable) and will slowly 
oscillate in ~5 meter altitude (on very high P value only, on small it's not 
noticeable). Affected by throttle a lot - won't hold altitude at all if 
throttle isn't inside hover range.
So, based on those observations - i would say alt hold does not work at all 
(but activation does something - at least copter tilts a bit to back when 
activating).

Original issue reported on code.google.com by Andrius....@gmail.com on 8 May 2013 at 7:29

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commit text for r315: 
Testversion ABLomas (Altitude Hold still needs work) 

Original comment by bouwens....@gmail.com on 20 May 2013 at 3:16