Created a function that branches calls to DOPAIR1 so that correct version is called. This decision is based upon whether MPI is running, vectorisation and orientation of the neighbouring cells.

Perform padding of the cache when populating it instead of on the fly. Create fake particles to be maxed out in the inner interaction loop.

Fixed bug with finding the exit iteration of the inner loops, -1 and +1 to value. Replaced vec_load with vec_unaligned_load for GCC. Pad cache correctly when the number of iterations of the inner loop is not a multiple of the vector length.

Timebin optimization

This implements a change to the active/inactive checks following @jwillis' remark that the code was a bit slower than in the old master he was working on. 

The idea is to pre-compute the largest active time-bin and then use this information to decide whether act on particles or not. The old scheme was computing the end-time of the particle which involves a lot more information for the same result.

See merge request !316

Made all python scripts numpy 1.8.2 compatible, and fixed some bugs while doing it.

Title says it all. This should close #272.

See merge request !319

Cleaned up GIZMO code, added SineWavePotential tests.

The GIZMO code should now be clean enough to merge with `master`, and to be used in scaling tests.

I have added 1-3D versions of a new SineWavePotential test, which tests gravitational hydrostatic equilibrium in an unphysical but convenient 1D periodic sine wave potential. This allows testing gravity + GIZMO hydro without running into boundary condition problems. Unfortunately, the non conservative form of the potential makes it impossible to test energy conservation in these tests. GIZMO can keep all three set ups stable with both an isothermal and an ideal gas equation of state. I have currently only tested with the exact Riemann solver, but the approximate solvers should work as well.

The code is still not stable enough to cope with the hydrostatic and disc patch tests; these are next on my list.

See merge request !317

Removed ideal gas specific SineWavePotential scripts and incorporated them in the isothermal script. Ideal gas now seems to work.