Fix LFI in proxy.php

Hi,

The file proxy.php is vulnerable to local file inclusion. It's possible to read any file from the filesystem; e.g. /etc/issue by requesting http://roomallocation.code4fun.de/proxy.php?q=/etc/issue, etc.

This fix checks that the file $_GET['q'] exists in the current directory, doesn't contains any "../" or null bytes.
Merge pull request #1 from nashe/patch-1

Fix LFI in proxy.php