Use real eigenvalue problems in roots() for complex chebfuns. about chebfun

[aaustin141]

Upon further consideration, this would not work well for functions like f(x) = x^2 + 1i*x, whose real parts have higher-multiplicity roots but which have only a single multiplicity root overall. There's a good chance that roots() will miss the higher multiplicity root of real(f) and return nothing while if we sought the single root of f directly, we would not have had any problems. See, e.g., the following example from Alex Townsend:

>> x = chebfun('x',[-2 sqrt(3)]);
>> f = x.^2 + 1i*x;
>> roots(f)
ans =
    -1.110223024625157e-16
>> roots(x.^2)
ans =
   Empty matrix: 0-by-1