[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
Merge pull request #956 from paparazzi/algebra_int_unsigned

[math] some cleanup and fixes for fixedpoint functions

Tested by @fvantienen and @flixr