Deletes filename. Similar to the Unix C unlink()
function. An E_WARNING level error will be generated on
Path to the file.
Note: Context support was added
with PHP 5.0.0. For a description of contexts, refer to
Returns TRUE on success or FALSE on failure.
On Windows, it is now possible to unlink() files with
handles in use, while formerly that would fail. However, it is still not
possible to re-create the unlinked file, until all handles to it have been