USING '..' ON WINDOWS
Backport of the fix to 5.0 (to be null-merged to 5.1).
Moved the test into the main test suite.
Made mysql-test-run.pl to not use symlinks for sdtdata as the symlinks
are now properly recognized by secure_file_priv.
Made sure the paths in load_file(), LOAD DATA and SELECT .. INTO OUTFILE
that are checked against secure_file_priv in a correct way similarly to 5.1
by the extended is_secure_file_path() backport before the comparison.
Added an extensive test with all the variants of upper/lower case,
slash/backslash and case sensitivity.
Added few comments to the code.
