Testing Helix fit code, chi2/dof
1. The working horse:
```
OUTPUT:

bool
HelixUtil::CircleFit(double x[],double y[], double wei[], int num){

//////////////////////////////////////////////////////////////////
// Circle fitting program
//
// This function will fit a circle to the points in the matrix x and y.
// 'num' is the number of points in x and y
// 'xc' is the found center in x
// 'yc' is the found center in y
// 'R' is the radius of the fitted circle
// 'chi2' error in fit
//
// Written by Mike Heffner Sept 21 1998
// error calculation added Oct 3 1998, Mike Heffner
// fit with point errors added May 1999 Holm Huemmler
//  Jan Balewski, January 2007
//  - fix chi2 formula,
//  - relace weights in x & y by common weigth, were merged  anyhow
//  - returns false only if # of points<4
//
// Fitting algorithm by: N.Chernov,G.Ososkov, Computer Physics
//          Communications 33(1984) 329-333
//////////////////////////////////////////////////////////////////
```

2. Input: segment of circle which matches a 10GeV Pt tracks at eta of 1.5, full filed.
* fixed params: R=66m; arc len=0.02 rad == ~120 cm;
sigL=1mm (along arc); sigR=0 (along radius), nd=10 equaly spaced points
weight[i]=const=1/sigL^2
* varied: location of the center of the circle uniform in 2pi (equivalent, to varied phi of the prim track)
* Gaussian noise added to each hit point along the arc.
* chi2/dof calculated as sum {recoR- dist(hit-recoCenter) /sigL }, squared
```example of one track (units=cm) & fit result

IN: 0 -23.50 -23.17
IN: 1 -32.86 -32.47
IN: 2 -42.26 -41.75
IN: 3 -51.77 -50.89
IN: 4 -61.34 -59.99
IN: 5 -70.87 -69.13
IN: 6 -80.30 -78.37
IN: 7 -89.79 -87.53
IN: 8 -99.32 -96.67
IN: 9 -108.91 -105.74
Fit: R=9207.21  xc=-6462.11 yc=6558.29 chi2dof=0.64692 nIter=2 len/cm=118.8
DEL: R=2607.21  xc=-1812.26 yc=1874.39
```
Few distributions for 1000 tracks

3. avr chi2/dof is 1

4. reco pT will have RMS of 40%, is non-Gaussian

5. Error of the curvature has Gaussian distribution

6. Make sure I added the sigL smearing correctly

7. Used macro doHelixA.C