can now save as 8bits png file

v4l2/grabvidseq.c

@@ -365,6 +365,12 @@ switch (foo) {
 	case FILE_TYPE_PNM:
 		foo = fimg_save_as_pnm(&cumul, outfile, 1);
 		break;
+	case FILE_TYPE_PNG:
+		foo = fimg_save_as_png(&cumul, outfile, 0);
+		break;
+	default:
+		fprintf(stderr, "can't save as %s\n", outfile);
+		break;
 	}
 	// free buffers
 fimg_destroy(&cumul);