Merge branch release-2018

Merge branch release-2018

Clashes in set_pull_init signature.

Issues with new pull checks from LocalAtomSet refactoring.

Transfered change to PME-on-GPU availability to new
location.

Ignored changes to pre-submit, because no longer appropriate.

Adopted changes to gmx solvate into master. The new test
coverage finds a memory leak that is fixed in this patch with
a refactoring of sort_molecule and add_solv.

Needed to include domdec/collect.h now used in master because
a function call from it was introduced in release-2018.

Change-Id: I5f7fcdf52a6093b455bd6e31c264696d88ced2ac