Support multiple files ("FileList" per FTS-1) in subj when creating .REQ files

Previously, this feature assumed just one request per FREQ message, however
FTS-1 make this clear:

      If  one  or more  of FileAttached, FileRequest, or  FileUpdateReq  are
      asserted  in an AttributeWord, the subject{72} field is interpreted as
      a  list of file specifications  which may include wildcards and  other
      system-dependent data.  This list is of the form

      FileList = [ FileSpec { Sep FileSpec } ] Null

      FileSpec = (* implementation dependent file specification.  may
                    not contain Null or any of the characters in Sep. *)

      Sep      = ( " " | "," )  { " " }

src/sbbs3/sbbsecho.c

@@ -5506,7 +5506,11 @@ void pack_netmail(void)
 			if((fp=fopen(req,"a")) == NULL)
 				lprintf(LOG_ERR,"ERROR %d (%s) creating/opening %s", errno, strerror(errno), req);
 			else {
-				fprintf(fp,"%s\n",getfname(hdr.subj));
+				char filelist[FIDO_SUBJ_LEN];
+				SAFECOPY(filelist, hdr.subj);
+				char* token;
+				for(token = strtok(filelist, " ,"); token != NULL; token = strtok(NULL, " ,"))
+					fprintf(fp,"%s\n",getfname(token));
 				fclose(fp);
 				if(write_flofile(req, addr,/* bundle: */false, cfg.use_outboxes, /* del_file: */true, hdr.attr))
 					continue;