Improve the way we define the time of the first snapshot and statistics in cosmology and non-cosmology modes.

Added direct calculation of the mesh forces when checking accuracy. Use higher-order CIC interpolation when translating the mesh back to the field tensors.

Better error messages for the case where the distance is 0 between two gparts. Only crash if the softening is also 0.

Free the offsets array at the end of the particle sorting routines.

See merge request !538

Master configuration options for the subgrid models

See merge request !537

Corrected comments and error message. Deal with the 'yes' option for subgrid schemes in a better way.

Print to stderr after  flushing stdout

Closes #413

See merge request !535

Speed up redistribute

See merge request !513

This reverts merge request !532

Add master option for subgrid model

Closes #422

See merge request !532

Allow the user to specify a non-standard path for the FFTW library at configure time.

See merge request !534

Escape the self-task recursion in the gravity sub-cell unskipping only if the cell has *no* gparts not if it has *some* gparts.

Improve unskip by escaping early

See merge request !528

Parallel initialisation

See merge request !533