Code review comment for lp:~ctjacobs-multiphase/fluidity/compressible-multiphase

Some more comments trickling through:

* assemble/Compressible_Projection.F90, line 463: dnvfrac_t is not used

* assemble/Compressible_Projection.F90, line 650,660: Why are we setting this
multiphase variable there, it's not used afaics and a bit confusing...

* assemble/Diagnostic_Fields_Matrices.F90, line 372: you query the timestep now
but it doesn't seem to be used? Also in the same routine you've added vfrac
and temp_vfrac that aren't used.

* calculate_compressible_continuity() looks good to me. Is it tested? Would a
better maybe be compressible_continuity_residual? As it's not directly clear
what "compressible_continuity" as a diagnostic quantity is...