Very simple 2D version working.  Force is softened by a plumber sphere of radius h and the artificial viscosity reverts to the default one (although MM should still work I think).
Cleanup of some outdated files.  Gravitational smoothing (2D) now done with a kernel rather than the plumber sphere.
Vorticity fix.
Fixed the 2D force so it's now 1/R as it should be for integrating equations over z.
Fixed the smoothing of gravitational force in 2D over the scale height of the disc.
Improved the smoothing on scale height in 2D.  Added SmoothingMultiple parameter.  When H_SMOOTHING is on in 2D, gravity will be smoothed to SmoothingMultiple*H.
Fixed up a bug in the Cullen & Dehnen artificial viscosity that caused it to crash in 2D.  Added output option OUTPUTSURFACE, which will output the surface density and scale height calculated using the 2D routine in 3D.