great-circle distance speedups

[yakra]

C++: store & retrieve segment length

Increases speed slightly when Computing stats & Creating per-traveler stats logs.
Along for the ride: added alternate great-circle distance formulas to Waypoint::distance_to & PlaceRadius::contains_vertex, commented out for now

[yakra]

http://forum.travelmapping.net/index.php?topic=3014.msg13843#msg13843
Added a commit to implement this in siteupdate.py.

On noreaster:

• Reading waypoints for all routes 116.9 -> 120.1 s, gaining 3.2 s.
• Computing stats 30.1 -> 26.1 s, losing 4.0 s.
  Let's call this moving 3.6+/-0.4 s from point A to point B. Times always seem to vary a little bit between runs in Python (for example, the total run time for all tasks other than the ones I measured for this benchmark went 260.2 -> 254.8 s); there will be a little noise in the signal.
• Creating per-traveler stats logs and augmenting data structure 46.2 -> 29.9 s. A 50% speedup for this task.

[yakra]

Spherical law of cosines formula for area graphs

253f752http://forum.travelmapping.net/index.php?topic=3014.msg13996#msg13996

Same as the existing formula, but with some terms factored out or simplified via trig identity.
Increases area graph generation speed by ~32%.

• Not such a big deal in C++ on BiggaTomato, where it gets us from 3.7 to 2.8 s.
• In Python on noreaster, we go from 56.8 to 43.1.

No DIFFs in the resulting graphs.

[jteresco]

Sorry I forgot this was here. Pulling in now and it will be used starting with tomorrow's site update. And thanks again for all the work on this.