message: Fix the 'clean' makefile target to remove the subdirectory
  'libmfem.x.x.x.dylib.dSYM' -- it was generating an error.
diff: @@ -517,7 +517,7 @@ $(ALL_CLEAN_SUBDIRS):
  $(MAKE) -C $(BLD)$(@D) $(@F)
  clean: $(addsuffix /clean,$(EM_DIRS) $(TEST_DIRS))
  - rm -f $(addprefix $(BLD),*/*.o */*~ *~ libmfem.* deps.mk)
  + rm -rf $(addprefix $(BLD),*/*.o */*~ *~ libmfem.* deps.mk)
  distclean: clean config/clean doc/clean
  rm -rf mfem/
  