Avoid build-time warning

[Erik Schnetter]

I see this warning when building. I assume this should instead be a run-time warning or error?

/Users/eschnett/Cbeta/arrangements/EinsteinEvolve/GRHydro_InitData/src/GRHydro_PoloidalMagFieldM.F90:110:2: warning: #warning "This algorithm does only work on Cartesian grids!!" [-Wcpp]
 #warning "This algorithm does only work on Cartesian grids!!"
  ^

Keyword:

[Ian Hinder]

If the results are always wrong, it should be a fatal error. If it is something that should be implemented, there could be a comment in the code and a ticket created.