Overlap in vkicker with certain parameters

[Laurie Nevay]

With the attached example, an elliptical beam pipe is constructed that overlaps with the magnet yoke in a vkicker.

angle = 0.64*mrad;
py = -sin(angle);

BVEX4E: vkicker, l=4*m, vkick=py, apertureType="elliptical", aper1=0.44*0.5, aper2=1.53*0.5, outerDiameter=1.7, vhRatio=1.34/2.84, hStyle=1, beampipeThickness=5*mm;

l1: line=(BVEX4E);

use, l1;

beam, particle="e-",
      energy=1.5*TeV;

[Laurie Nevay]

Fixed. The calculation for the dipole parameters failed in some niche cases where the beam pipe was highly asymmetric and comparable to the magnet size, and for a vertically orientated dipole.

The calculation has been revised and is clearer. Sensible geometry is now produced and does not overlap.

These parameters have been added to a test as this didn't show up in regular testing.

![Screen Shot 2018-07-26 at 15.07.58.png] (https://bitbucket.org/repo/x9yz88/images/4080611735-Screen%20Shot%202018-07-26%20at%2015.07.58.png)