File name validation

There are a couple of security issues related to file names

1. Prevent renaming foo.jpg to foo.php.jpg. See file_munge_filename

2. Forbid some characters(combos): /, \, :, ../, dots at the beginning/end, invalid chars in some operating systems(*?"<>), null

3. Limit filename length

4. Check existence of the new name (on php side)