This adds more tests for unsuported features.

-x test in current form fails (under some conditions); the change works
almost - currently it fails if test directory is on SAMBA (or, probably, any
network) drive.

-N does not work on Cygwin. I mailed cygwin list as it looks like a bug
(AFAIK both FAT/NTFS support notion of different access and modification
times).

/dev/fd is not supported on Cygwin so -e and -O obviously failed. Manual
says, that it is emulated - but I am not sure, in which context it can be
used.

-andrej