[math] int32_sqrt returns unsigned int

and takes unsigned int as arg
[state interface] speed_norm_i is unsigned
[rotorcraft] navigation: unsigned nav_leg_length
[math] fix int32_vect2_normalize

keep correct sign of vector
[tests] show warnings by default
[simulator] OCaml sim: simulate sys_time

should fix #962
[rotorcraft] datalink: check ac_id of RC_4CH message

should fix at least some of the problems described in #965
[omap] Added linux i2c driver