Handle READ_GAP_ROOT as an "outer loop"

in the sense of the message "you can 'quit;' to quit to outer loop" in
break loops. I.e. continue in READ_GAP_ROOT even if `UserHasQuit`.

src/streams.c

@@ -407,8 +407,13 @@ Int READ_GAP_ROOT ( const Char * filename )
     if (OpenInput(&input, path)) {
         while (1) {
             ExecStatus status = ReadEvalCommand(0, &input, 0, 0);
-            if (STATE(UserHasQuit) || STATE(UserHasQUIT))
+            if (STATE(UserHasQuit)) {
+                FlushRestOfInputLine(&input);
+                STATE(UserHasQuit) = FALSE;
+            }
+            else if (STATE(UserHasQUIT)) {
                 break;
+            }
             if (status == STATUS_RETURN) {
                 Pr("'return' must not be used in file", 0, 0);
             }