DONOTMERGE: Purge communicator before free on mpich4+#787

vehre wants to merge 1 commit intovehre/issue-783-fix-copy-selfsourceryinstitute/OpenCoarrays:vehre/issue-783-fix-copy-selffrom

vehre/issue-781-clear-communicator-4-mpichsourceryinstitute/OpenCoarrays:vehre/issue-781-clear-communicator-4-mpichCopy head branch name to clipboard