Compiler warning fixes

Here is another set. 

Some additional questions:
- How do you want to handle unused variables? My tendency is to delete them, with the thinking that if they are not used then who knows how valid the values they hold are. Other option is to just comment out.
- What to do about the "Frame size of NNNN is larger than 1024 bytes" warnings? Are these frame size checks valid, or should the warning just be turned off?
Didn’t realize that get_bearing_to_next_waypoint takes doubles. This should all go up to double. I’ll fix.

On Jul 6, 2014, at 5:08 AM, Lorenz Meier <notifications@github.com> wrote:

> In src/lib/geo/geo.c:
> 
> > @@ -297,12 +297,12 @@ __EXPORT int get_distance_to_arc(struct crosstrack_error_s *crosstrack_error, do
> >  		// TO DO - this is messed up and won't compile
> >  		float start_disp_x = radius * sinf(arc_start_bearing);
> >  		float start_disp_y = radius * cosf(arc_start_bearing);
> > -		float end_disp_x = radius * sinf(_wrapPI(arc_start_bearing + arc_sweep));
> > -		float end_disp_y = radius * cosf(_wrapPI(arc_start_bearing + arc_sweep));
> > -		float lon_start = lon_now + start_disp_x / 111111.0f;
> > -		float lat_start = lat_now + start_disp_y * cosf(lat_now) / 111111.0f;
> > -		float lon_end = lon_now + end_disp_x / 111111.0f;
> > -		float lat_end = lat_now + end_disp_y * cosf(lat_now) / 111111.0f;
> > +		float end_disp_x = radius * sinf(_wrapPI((double)(arc_start_bearing + arc_sweep)));
> This looks like we need a different approach here, since first casting to (soft) double and then using the single precision sinf() call is not consistent.
> 
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