Can now just load

[jvoight]

Tore out the requirement to update Magma. Unfortunately, certain functions still need to be overridden, but we now just do this by loading them in the spec file. This will cause an issue if these are updated in future release of Magma. But in the meantime, this works:

AttachSpec("spec");
sigma := [Sym(4) | (1,2,3,4), (1,3,4,2), (1,3,4)];
Gamma := TriangleSubgroup(sigma);
X, phi := BelyiMap(Gamma);