Merge branch 'sink_merger2' into 'master'

src/Makefile.am

src/cell.c

src/cell.h

src/cell_convert_part.c

src/cell_drift.c

src/cell_sinks.h

src/cell_unskip.c

src/engine.c

src/engine_maketasks.c

src/engine_marktasks.c

src/runner.h

src/runner_doiact_functions_sinks.h

src/runner_doiact_functions_sinks_merger.h

src/runner_doiact_sinks_merger.c

src/runner_doiact_sinks_merger.h

src/runner_main.c

src/runner_others.c

src/scheduler.c

src/sink.h

src/sink/Default/sink_iact.h