Do not pass the (now unused) time-step send/recv tasks to the hydro and gravity communication creation functions.

Only construct the send/recv tasks for a hydro/gravity when required by the type of cell in the proxy.

Corrected typo in Minimal-SPH implementation that prevents neighbour number convergence in some cases.

Make sure the code compiles with vectorization switched on and using a different hydro scheme from Gadget-2.

Use a different criterion for gravity or hydro to construct the proxies corresponding to a given cell.

Fixed a moronic bug. Unskipping MPI sends and recvs for gravity should not be done *only* for local pairs. Obviously....