Check that an error is not created due to rounding with GCC 7.2.0.

Closes #400

See merge request !514

Increase HDF5 chunk size and set shuffle filter for single and serial output when compression is switched on.

Cosmological terms in vectorized version of Gadget SPH.

Closes #406

See merge request !510

Pass the cosmological model to the cooling function and get the physcial density and internal energy.

Cosmological time integration

See merge request !509

Re-instate the explicit casts after malloc in proxy.c that had disappeared by mistake in a bad merge. Matthieu be more carefulgit status!

Might be better to use a --with argument so that external builds can be located more easily in non-standard places