\w could match multibyte chars depending on system setup

crypt seems to behave different on different systems when the salt
is empty.

This allows to treat empty parameters as default

This new wrapper ensures types are correct and accessed parameters are
actually set (with custom default fallbacks).

The wrapper is available in the global $INPUT variable. It accesses
$_REQUEST by default. If POST or GET is required, the post and get
members can be used:

$INPUT->int('foo',false); // access $_REQUEST['foo'], default false
$INPUT->post->int('foo'); // access $_POST['foo'], default 0
$INPUT->get->int('foo'); // access $_GET['foo'], default 0

The codebase still needs to be updated to make use of this.

Fix for FS#2522 / Now all places of $lang['restored'] are covered with the restored-date information

This also fixes a problem wiht PHP 5.4 when there is metadata but the
date key is empty.

This bug occurs on systems where writing a zero-length string to an
empty file does not update the file's modification timestamp.

This leads to the messages.txt being downloaded almost endlessly, causing
long delays for logged-in users. Visitors are not affected, because the
messages.txt is only updated for logged-in users.