Fix more leaks

- get_parent_pid: free buffer returned from read_line after use.
 - workspace_for_pid: ensure free_pid_workspace is called when
   pid_workspaces are removed from config->pid_workspaces.
 - cmd_split: return the cmd_results from _do_split, so that the
   parent function may free it.

common/util.c

@@ -96,6 +96,7 @@ pid_t get_parent_pid(pid_t child) {
 			parent = strtol(token, NULL, 10);
 		}
 
+		free(buffer);
 		fclose(stat);
 	}