Mitigation for file reverse

Filter for all characters that make directory traversal possible.

That means not just '.' and '/', but also any encoded alternatives such as:

%2e%2e%2f = ../

%2e%2e/ = ../

..%2f = ../

..%c0%af = ../ 

The best way to mitigate directory traversal is not to use user input when making file system calls. Of course, that may not be possible, so an alternative is to use an index. 

Example: 

view.php?language=English

—> 

view.php?language=1