Conflicts:
        src/engine.c

Autotools update

Updates for issue #181. Still need to do some testing if tcmalloc is better.

See merge request !190

Useful when profiling.

Previously shared libraries were linked using the unwrapper compiler (so MPI special flags didn't work)

The entropy_in_IC flag is now set and read correctly. Restart from snapshot is possible.

Fix to #178. 

This is a rather temporary fix but allows full compatibility with Gadget. We can now restart from a snapshot and also run for a while with Gadget, then with SWIFT, then with Gadget and so on.

See merge request !189

One major change to replace all gpart id/parts with the new id_or_neg_offset.

As discussed in #123, this merge request changes the `gpart.id` and `gpart.part` anonymous union into a single `long long int id_or_neg_offset`.

If this number is positive, then it is the particle ID and the `gpart` has no hydro counterpart.

If this number is negative, then it is the offset in the `parts` array of this particle's hydro counterpart.

See merge request !118

Tidy up so that both trees use the same library dependencies

Set the super-cell to the first cell with interactions.

The super cell is either a non-empty leaf or the first cell for which an interaction task is defined. need to add a condition for gravit tasks once these have been settled.

Separating this from the `mpi_skip` branch as it is not really related and should be tested separately.

See merge request !186

Conflicts:
	src/debug.c
	src/debug.h
	src/engine.c
	src/gravity/Default/gravity_debug.h
	src/gravity/Default/gravity_part.h
	src/hydro/Gadget2/hydro_debug.h
	src/part.h
	src/runner.c
	src/tools.c
	src/tools.h

the super cell is either a non-empty leaf or the first cell for which an interaction task is defined. need to add a condition for gravit tasks once these have been settled.

add a third communication step which exchanges the particles after the kick, just to make sure we have the correct ti_end_min values for each foreign cell.

link the send/recv tasks to all their cells and sub-cells. first step in linking send/recv tasks to density/force tasks.

Remove the part<->gpart link checks. These can be un-commented back in when debugging.

As discussed during the meeting, here are some tests that are non-necessary in serious runs.



See merge request !185

Coding style

Sorry Peter here is another big annoying one. 

 - Improved the code quality in `runner_doiact.h` to match the coding standard used elsewhere: declare variable only where they are needed and use constants where possible.
 - Modified many headers to avoid long unnecessary inclusion lists. Should speed up compilation.

Thanks !

See merge request !182