* psxreaddir/psxreaddir.scn, psxreaddir/test.c: Do not test for
rewinddir(NULL) since we are now using newlib's implementation and it
does not check for NULL. This causes a fault on some targets.
* psxmount/test.c, psxmount/psxmount.scn: Improve output to report
expected error condition in one case.
* psxreaddir/test.c, psxreaddir.scn: Added test cases to exercise
readdir() of root of mounted filesystem. Also corrected the screen
file for some mistakes noticed in this effort.
